I have faced same issue recently and fixed it by applying small work around in it. See…the module I purchased (plz check your module) is (ONLY) “RS232” interface with modem, NO TTL compatibility.
The problem I faced was, the module supported to communicate via HyperTerminal, but no response when I tried with TTL logic (ie. via 89c51). Then I bye-passed the wires runing out from MAX232 (Note: to communiate in TTL logic, we do NOT require the help of MAX232, if you don’t want you may remove from the board), to the pin 11 and 12 of MAX232 and connect with RX & TX of MC respectively. Now it is working….!
Thank you.
Muthu Kumar G.