VB.net sending/recieving AT commands from SIM Card

ok, so i have been using Vb for a while but brand new to communicating with devices.

I have a HP Elitebook 820 which has a SIM card slot, what i'd like to do is read and display the SIM card info - specifically the serial number. I have done a bit of searching and found lots of people talking about AT commands. after a bit more searching i gave it a try.

Code:

---

Dim com1 As SerialPort = New System.IO.Ports.SerialPort

    com1.PortName = "COM6"

    com1.Open()

    If com1.IsOpen Then
        com1.Write("AT+CIMI")
        Dim result As String
        result = com1.ReadExisting
        MsgBox(result)
    Else
        MsgBox("port not open")
    End If

---

No Errors but just blank string returned. Could anyone help me out? i was told that i would have to go through all the responses from the port but i dont really know what this means

i'd guess that at the time you sent "AT+CIMI" and then read existing the devices response has not yet arrived. you can simply put a 1 second delay after the write to see if this assumtion is true. for final code you should change this to more clever approches with threads/events.
(untested)

Code:

---

Dim com1 As SerialPort = New System.IO.Ports.SerialPort

    com1.PortName = "COM6"

    com1.Open()

    If com1.IsOpen Then
        com1.Write("AT+CIMI")
        Threading.Thread.Sleep(1000)
        Dim result As String
        result = com1.ReadExisting
        MsgBox(result)
    Else
        MsgBox("port not open")
    End If

---