Communication between GSM and Arduino

Hello There !

Have SIM900A GSM Module with RS-2332 with extra pins for Tx. Rx. and GND.
Tested the modem with the AT Command Tester. It is functioning OK.
uploaded the test code in Arduino to dial a number from the GSM modem to Cell
In serial Monitor it displays the Cell No. ATD91xxxxxxxxxx number and after time delay ATH
But does not dial the number to the cell.
The GSM and Arduino are connected as per the manufacturer's instructions i.e.

GSM Tx. to Arduino Rx.,
GSM Rx. to Arduino Tx;
GSM Gnd to Arduino Gnd

The connecting jumpers between the GSM Module and Arduino are checked, it is OK
Checked with other Arduino Board also but no response

Plz. help me to resolve this problem