For my SIM900 powered GPRS Shield V2.0 from seed  I needed to find a suitable cell phone provider. This proved to be more complex than I thought. I should point out that I am located in the USA. Cellular networks are different all over the world and what I write in this article may not be true for other countries.
For starters, it’s important to understand that some cellular providers do not support GSM at all. Verizon for instance is CDMA only. I learned this the hard way after purchasing a prepaid SIM card for Verizon. AT&T ended up being my go-to provider for my little gadgets. Their go phone SIM cards always did the trick for me. You can buy these online. My local At&T store actually kindly provided me with a hand full of inactive SIM cards free of charge. Those cards are useless until activated.
To activate a AT&T go SIM card, go visit the AT&T activation page.
To activate your At&T go SIM card simply enter the SIM card number and follow the prompts. One catch is that you need to have the IMEI number of your device. SIM800 or SIM900 powered modules have the IMEI printed directly on the GSM module. However, AT&T determines what plans they offer you based on the IMEI number. If you enter the actual IMEI of the GSM module, odds are you’re only going to get monthly data and text plans. Currently the cheapest is $ 45 / month for unlimited call and text plus 1 GB of data. This is good if you intend to use the GPRS functionality of the module. But if you only intend to use the text / call functionality sporadically, there’s more suitable plans available. The easiest pan to “unlock” these plans is to enter the IMEI of an old AT&T go phone. Don’t have one? Here’s one:
After the activation is complete, the website will show you your new phone number. Now only add money to the account and your device is ready to be connected to the cellular network. That’s it, it’s that simple.
WARNING: Many providers, such as AT&T, intend to shut down their 2G (GSM) and 2.5G (GPRS) networks in the very near future. AT&T announced this shutdown to be completed by the end of 2016. So if you’re developing a new product, this technology may not be the best to bet on.
Links and Sources:
 GPRS Shield V2.0, Seed: http://www.seeedstudio.com/depot/GPRS-Shield-V20-p-1379.html