My Program Freezes when sending a message using gsm shield VB.net - vb.net

Question

My program is hangs when sending a messsage my code show no error and when i am testing my gsm shield in hyperterminal i can send message and recieve it through my phone using AT commands. But in my program it just freezes.
Imports System
Imports System.Threading
Imports System.ComponentModel
Imports System.IO.Ports
Public Class Form1
'connect your mobile/GSM modem to PC,
'then go in device manager and check under ports which COM port has been slected
'if say com1 is there then put com2 in following statement
Dim SMSEngine As New SMSCOMMS("COM4")
Dim i As Integer
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
SMSEngine.Open() 'open the port
SMSEngine.SendSMS() 'send the SMS
End Sub
End Class
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)
'initialize all values
SMSPort = New SerialPort
With SMSPort
.PortName = COMMPORT
.BaudRate = 9600
.Parity = Parity.None
.DataBits = 8
.StopBits = StopBits.One
.Handshake = Handshake.RequestToSend
.DtrEnable = True
.RtsEnable = True
.NewLine = vbCrLf
End With
End Sub
Public Function SendSMS() As Boolean
If SMSPort.IsOpen = True Then
'sending AT commands
SMSPort.WriteLine("AT")
SMSPort.WriteLine("AT+CMGF=1" & vbCrLf) 'set command message format to text mode(1)
SMSPort.WriteLine("AT+CSCA="" [phone]""" & vbCrLf) 'set service center address (which varies for service providers (idea, airtel))
SMSPort.WriteLine("AT+CMGS= + TextBox1.text + " & vbCrLf) ' enter the mobile number whom you want to send the SMS
_ContSMS = False
SMSPort.WriteLine("+ TextBox1.text +" & vbCrLf & Chr(26)) 'SMS sending
MessageBox.Show(":send")
SMSPort.Close()
End If
End Function
Public Sub Open()
If Not SMSPort.IsOpen Then
SMSPort.Open()
End If
End Sub
Public Sub Close()
If SMSPort.IsOpen Then
SMSPort.Close()
End If
End Sub
End Class

Answer 1

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
SMSEngine.Open() 'open the port
If Not BackgroundWorker1.IsBusy Then
BackgroundWorker1.RunWorkerAsync()
End If
End Sub
Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
If SMSPort.IsOpen = True Then
'sending AT commands
SMSPort.WriteLine("AT")
SMSPort.WriteLine("AT+CMGF=1" & vbCrLf) 'set command message format to text mode(1)
SMSPort.WriteLine("AT+CSCA="" [phone]""" & vbCrLf) 'set service center address (which varies for service providers (idea, airtel))
SMSPort.WriteLine("AT+CMGS= + TextBox1.text + " & vbCrLf) ' enter the mobile number whom you want to send the SMS
_ContSMS = False
SMSPort.WriteLine("+ TextBox1.text +" & vbCrLf & Chr(26)) 'SMS sending
MessageBox.Show(":send")
SMSPort.Close()
End If
End Sub