There are 2 main competing network technologies: Global System for Mobile Communications (GSM) and Code Division Multiple Access (CDMA), although CDMA is becoming more obselete in Australia. GSM and CDMA will allow you to choose a carrier that uses the preferable network technology for your needs. And 3G is the third generation of tele standards and technology for mobile networking. The main difference between GSM & CDMA is that GSM uses SIMs & CDMA does not. 3G is the currently the fastest mobile internet networkk available. GSM is considered the "world standard" whereas CDMA is not.