sending sms to multiple recipients using gsm in vb.net - vb.net

Question

Imports System
Imports System.Threading
Imports System.ComponentModel
Imports System.IO.Ports
Public Class SMSCOMMS
Private WithEvents SMSPort As SerialPort
Private SMSThread As Thread
Private ReadThread As Thread
Shared _Continue As Boolean = False
Shared _ContSMS As Boolean = False
Private _Wait As Boolean = False
Shared _ReadPort As Boolean = False
Public Event Sending(ByVal Done As Boolean)
Public Event DataReceived(ByVal Message As String)
Public Sub New(ByRef COMMPORT As String)
SMSPort = New SerialPort
With SMSPort
.PortName = COMMPORT
.BaudRate = 115200
.Parity = Parity.None
.DataBits = 8
.StopBits = StopBits.One
.Handshake = Handshake.RequestToSend
.DtrEnable = True
.RtsEnable = True
.NewLine = vbCrLf
End With
'ReadThread = New Thread(AddressOf ReadPort)
End Sub
Public Sub SendSMS(ByVal CellNumber As String, ByVal SMSMessage As String)
Dim MyMessage As String = Nothing
If SMSMessage.Length <= 160 Then
MyMessage = SMSMessage
Else
MyMessage = Mid(SMSMessage, 1, 160)
End If
If IsOpen = True Then
SMSPort.WriteLine("AT+CMGS=" & CellNumber & vbCr)
_ContSMS = False
Thread.SpinWait(200)
SMSPort.WriteLine(MyMessage & vbCrLf & Chr(26))
_Continue = False
Thread.SpinWait(200)
RaiseEvent Sending(False)
End If
End Sub
Private Sub ReadPort()
Dim SerialIn As String = Nothing
Dim RXBuffer(SMSPort.ReadBufferSize) As Byte
Dim SMSMessage As String = Nothing
Dim Strpos As Integer = 0
Dim TmpStr As String = Nothing
While SMSPort.IsOpen = True
If (SMSPort.BytesToRead <> 0) And (
SMSPort.IsOpen = True) Then
While SMSPort.BytesToRead <> 0
SMSPort.Read(RXBuffer, 0, SMSPort.ReadBufferSize)
SerialIn =
SerialIn & System.Text.Encoding.ASCII.GetString(
RXBuffer)
If SerialIn.Contains(">") = True Then
_ContSMS = True
End If
If SerialIn.Contains("+CMGS:") = True Then
_Continue = True
RaiseEvent Sending(True)
_Wait = False
SerialIn = String.Empty
ReDim RXBuffer(SMSPort.ReadBufferSize)
End If
End While
RaiseEvent DataReceived(SerialIn)
SerialIn = String.Empty
ReDim RXBuffer(SMSPort.ReadBufferSize)
End If
End While
End Sub
Public ReadOnly Property IsOpen() As Boolean
Get
If SMSPort.IsOpen = True Then
IsOpen = True
Else
IsOpen = False
End If
End Get
End Property
Public Sub Open()
If IsOpen = False Then
SMSPort.Open()
'ReadThread.Start()
End If
End Sub
Public Sub Close()
If IsOpen = True Then
SMSPort.Close()
End If
End Sub
End Class
i tried sending sms using gsm modem in vb.net using this code. This is working fine but when i tried sending sms to multiple recipient the first recipient only receives the sms while the others no reponse.
This is the code for the sending sms:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim sms As SMSCOMMS
sms = New SMSCOMMS("COM25")
sms.Open()
sms.SendSMS("+63*******", "123")
Threading.Thread.SpinWait(200)
sms.SendSMS("+63*******", "456")
sms.Close()
End Sub