Public Class Form1
    Dim mySerialPort As New System.IO.Ports.SerialPort
    Delegate Sub DataShow(ByVal myString As String)

    Private Sub Button1_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button1.Click
        mySerialPort.Write("at+wmsn" & vbCrLf)
    End Sub

    Private Sub Form1_Disposed(ByVal sender As Object,ByVal e As System.EventArgs) Handles Me.Disposed
        If mySerialPort.IsOpen Then
            mySerialPort.Close()
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles MyBase.Load
        With mySerialPort
            .PortName = "COM3"
            .DataBits = 8
            .StopBits = IO.Ports.StopBits.One
            .Parity = IO.Ports.Parity.None
            .BaudRate = 115200
            .RtsEnable = True
            .ReceivedBytesThreshold = 1
            AddHandler mySerialPort.DataReceived,AddressOf SerialPort_DataReceived
            .Open()
        End With
    End Sub

    Sub SerialPort_DataReceived(ByVal sender As Object,ByVal e As System.IO.Ports.SerialDataReceivedEventArgs)
        Dim sp As IO.Ports.SerialPort = sender
        Dim s As String = sp.ReadExisting
        Invoke(New DataShow(AddressOf SerialPort_DataShow),New Object() {s})
    End Sub

    Private Sub SerialPort_DataShow(ByVal myString As String)        
        TextBox1.Text = TextBox1.Text & myString
    End Sub
End Class