Sorry to hijack the thread, but its kinda old anyway.
Im having an issue with my SIM900. I posted the details here:
http://forum.arduino.cc/index.php?topic=427874.msg2949059#msg2949059
But in essence, the sim900 works with a mega using a library. And it has worked a few times for me using at commands similar to the ones mentioned in this thread. But most of the time it doesnt work because no sms gets sent.
Im stumped. Please help!