The SIM900 is the GSM module that we ultimately use on our PCB. We didn’t use it for debugging since there are no supported sockets for it – it had to be soldered onto the board. A friend of ours gave us a spare SIM900 that he had, which was lucky for us since at the time we started this project, all SIM900 modules and evaluation boards were out of stock! We chose to move from the sm5100b to the sim900 because of documentation. There is a well written hardware reference design for the 900 as well as multiple software support documents.
http://www.micro4you.com/store/sim900-gprs/gsm-module.html (unsure if the board comes with the module attached)
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