GSM communication with static IP via GPRS?

I'm new to GSM technology. I have read some notes about GSM. But still find a place to settle into GSM. My project is about, microcontroller which reads some data and i have to send that data using GSM modem to static IP address. How to do that? Please help. Also i thought of buying SIM900 module. Well, is it good? (or) do i have to switch over to any other module?

I have looked into website sim.com. There are many module SIM900, SIM900B, SIM900D, SIM900S. Which one i have to buy? what are the differences between them?

Do i have to use RS232 to interface with SIM900?

Please help!!!

 

can i use only AT commands? or do i have to learn TCP/IP protocol?

 

Any help? please