I have some problems with SMS sending with MSComm. Please somebody help me!

Here is my code in VB:

If Not comSiemens.PortOpen Then comSiemens.PortOpen = True
comSiemens.Output = "AT+CMGS=" & Chr$(34) & <MobileNumber> & Chr$(34) &
vbCr
' MsgBox "Hit OK!", vbOKOnly
txtInput.Text = comSiemens.Input
comSiemens.Output = <SMSText> & Chr$(26) & vbCr
txtInput.Text = txtInput.Text & vbCrLf & comSiemens.Input & vbCrLf & "Done..."
If comSiemens.PortOpen Then comSiemens.PortOpen = False

with commented MsgBox I have only 6 characters back with MSCommx.Input:
AT+CMG

with uncommented MsgBox I have the full answer and SMS also sent correctly

My question:
How I can get correct feedback and good SMS posting WITHOUT MsgBox. I also
thanks other solutions as well!