SMS remains a tool that is used by millions of people everyday since 1993,recently I was asked to develop a cross platform application that will send sms to people on their bills due date. I had an old 3G USB stick lying around just like the one in the picture below :

3g modem

I thought I might use it to send sms.I have played before with sms using a set of Delphi components ( NrComm Lib ) but Delphi as you know is not cross platform , neither the components are free. Buying components is just not my style … I live in Romania if you lived here it probably wasn’t your style too. So I decided to write my own sms unit to achieve this purpose.I found some examples on sending sms using Lazarus and I have decided to test if the device works properly. I had the surprise of the device giving me an error every time I tried to send sms. But researching I saw that are two ways that the modem accepts sms messages ( text mode and pdu mode ) . Tried to send sms using pdu mode using the components I mentioned before and worked flawless, then I took the decision to write my unit to send sms in pdu mode.

The result is down bellow , use it how you wish if you got time improve it to receive sms,send mass sms etc.It uses the SynaSer library for interacting with the COM port

 Delphi | 
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unit usms_sender;
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{$mode objfpc}{$H+}
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interface
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uses
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  Classes, SysUtils,SynaSer;
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type
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  TByteArray = array of Byte;
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  ESMSException = class (Exception);
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  TSMS = class (TObject)
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  private
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  sms : String;
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  phone : String;
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  pdu_string : String;
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  phone_len : Integer;
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  serial : TBlockSerial;
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  connected : Boolean;
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  function  IsNumeric(const S : String) : Boolean;
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  procedure SetPhone(pho : String);
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  procedure EncodeToGsmAlphabet(const ascii : String;out tmp : TByteArray);
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  procedure Digest;
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  function  PackPhoneNumber : String;
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  function  AsciiToPdu(const ascii : String) : String;
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  procedure SetSms(S : String);
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  public
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  constructor Create(const smsx : String; phonex : String);overload;
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  constructor Create();
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  destructor Destroy;override;
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  procedure Send;
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  procedure ConnectModem(const port : String; baud : Integer = 115200);
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  procedure DisconnectModem;
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  published
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  property txtSMS : String read sms write SetSms;
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  property txtPhone : String read phone write SetPhone;
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  end;
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implementation
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procedure TSMS.Digest;
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var
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  tmp : String;
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begin
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    tmp := AsciiToPdu(sms);
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    pdu_string:='001100' + IntToHex(phone_len,2) +'91' + PackPhoneNumber + '0000AA' + IntToHex((Length(sms)),2) + tmp ;
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end;
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destructor TSMS.Destroy;
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begin
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    DisconnectModem;
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    inherited;
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end;
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procedure TSMS.DisconnectModem;
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begin
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    if connected then
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    begin
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      if Assigned(serial) then
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      begin
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      serial.CloseSocket;
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      serial.Free;
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      end;
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      connected := false;
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    end;
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end;
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procedure TSMS.ConnectModem(const port : String; baud : Integer = 115200);
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begin
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    serial := TBlockSerial.Create;
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    serial.Config(baud,8,'N',1,false,true);
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    serial.Connect(port);
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    serial.ATCommand('AT');

 Delphi | 
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     Sleep(100); // I am not a fan of hardcoded sleep but it takes a while until the modem responds

 Delphi | 
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   <!--DVFMTSC-->connected := serial.ATResult;
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    if not connected then
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    begin
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    serial.Free;
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    raise ESMSException.Create('Modem is not responding!');
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    end;
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end;
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procedure TSMS.SetSms(S : String);
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begin
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    if Length(S) > 160 then raise ESMSException.Create('Message is to large!');
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    sms := S;
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end;
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function PackBytes(a,b : Byte) : Byte;
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begin
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    Result := (b shl 4) or a;
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end;
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procedure TSms.Send;
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begin
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    if connected then
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    begin
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    Digest;
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    serial.ATCommand('AT+CMGF=0');
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    serial.ATCommand('AT+CMGS=' + IntToStr(Length(pdu_string) div 2 - 1));
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    serial.SendString(pdu_string + #$1A);
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    end
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    else raise ESMSException.Create('No modem connected!');
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end;
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function TSms.PackPhoneNumber() : String;
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var
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  i : Integer;
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begin
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  Result := '';
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  for i := 1 to (Length(phone) div 2)  do
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      Result := Result + IntToHex(PackBytes(StrToInt('$'  + phone[(i * 2) - 1]),StrToInt('$' + phone[(i * 2)])),2);
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end;
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procedure TSMS.EncodeToGsmAlphabet(const ascii : String;out tmp : TByteArray);
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var
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  i : Integer;
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  j : Byte;
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const
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  gsm7Bit: array [0 .. 127] of Byte = (64,163,36,165,232,223,249,236,242,199,10,216,248,13,197,229,0,95,0,0,0,0,0,0,0,0,0,0,198,230,223,201,32,33,34,35,164,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,161,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,196,204,209,220,167,191,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,228,246,241,252,224);
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begin
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  SetLength(tmp,0);
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  for i := 1 to Length(ascii) do
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  begin
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      for j := 0 to 127 do
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          if (gsm7Bit[j] = Ord(ascii[i])) then
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          begin
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            SetLength(tmp,Length(tmp) + 1);
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            tmp[High(tmp)] := j;
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            break;
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          end;
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  end;
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end;
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function ByteToBin(Value: Byte): string;
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var
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  i: Integer;
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begin
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  Result := '';
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  for i := 6 downto 0 do
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    if Value and (1 shl i) <> 0 then
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      Result := Result + '1'
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  else
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    Result := Result + '0';
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end;
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function BinToInt(Value: string): Byte;
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var
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  i : Integer;
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begin
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  Result := 0;
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  for i := 8 downto 1 do
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    if Value[i] = '1' then Result := Result + (1 shl (8 - i));
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end;
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function TSMS.AsciiToPdu(const ascii : String) : String;
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var
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  bts : TByteArray;
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  bin,tmp: string;
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  total : TStringList;
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  i,len : Integer;
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begin
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  Result := '';
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  EncodeToGsmAlphabet(ascii,bts);
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  total := TStringList.Create;
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  for i:=Low(bts) to High(bts)do
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  begin
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    bin := ByteToBin(bts[i]);
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    total.Add(bin);
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  end;
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  for i:=0 to total.Count -2  do
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  begin
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      len := 8 - Length(total[i]);
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      if len = 8 then
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      begin
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          total[i] := '11111111';
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          Continue;
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      end;
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      if len >0 then
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      begin
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      tmp := total[i+1];
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      bin := Copy(tmp,Length(total[i + 1]) - len+1,len);
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      tmp := total[i];
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      Insert(bin,tmp,1);
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      total[i] := tmp;
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      bin := Copy(total[i+1],1,7 - len);
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      total[i+1] := bin;
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      end;
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  end;
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  for i := 0 to total.Count - 1 do
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  begin
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    tmp := total[i];
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    if tmp = '' then Continue
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    else if Length(tmp) < 8 then
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      tmp := IntToHex(0,8-Length(tmp)) + tmp
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    else if (BinToInt(tmp) > 254) then Continue;
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    Result := Result + IntToHex(BinToInt(tmp),2);
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  end;
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  total.Free;
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end;
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procedure TSMS.SetPhone(pho : String);
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begin
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    if not (IsNumeric(pho)) then raise ESMSException.Create('Invalid phone number. Must be in international format eg 40741966242');
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    phone_len:= Length(pho);
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    if odd(Length(pho)) then
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    phone := pho + 'F'
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    else
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    phone := pho;
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end;
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function TSMS.IsNumeric(const S: String) : Boolean;
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var
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  c : Char;
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begin
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    Result := True;
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    for c in S do
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        if not (c in ['0'..'9']) then
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        begin
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          Result := False;
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          break;
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        end;
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end;
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constructor TSMS.Create(const smsx : String; phonex : String);
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begin
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    inherited Create;
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    SetPhone(phonex);
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    SetSms(smsx);
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end;
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constructor TSMS.Create;
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begin
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    inherited Create;
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end;
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end.
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