Lpc2000

Dear frends,

I have MCB2140 board from KEIL and I want to connect MC35i GSM modem
with the same on COM1 of lpc2148.

The port given on board is not fully connected as there are only two
wires connected Tx and Rx. I want to make a data call to another PC
and the at command is ATD<NUMBER>

Problem is if i m transmitting this at command or say any data from
board to PC using serial comm, I can receive that on PC.
But when i am sending same command to GSM modem from my board I am not
getting any responce resulting there is no ring to the other modem
which is connected to PC.

I want to do it with two wire only so need your help..

Please please guide me

Pankaj