If you use a SIM card you are on the GSM network. If you use Telestial it should be GSM. GSM actually means global system for mobile and is the most popular one in the world. That's why when you have a CDMA cell phone (like Verizon uses) you can't take it to many places out of the country (USA), basically only some parts of Canada and Mexico. CDMA means Code Division Multiple Access, basically it was created to utilize digital I believe (on that I may be incorrect) and I am going to shut up now as I sound like a giant geek. But yeah basically unless you are trapped in the US you should have GSM as it's what most international countries use.