3G is referencing the technology/chip the iPhone uses to connect to the internet when WiFi is not available. It is a several years old and several times faster technology than the EDGE technology/chip that the current iPhone uses.
So why EDGE is called 2.5G then, and GSM was called 2G? ;p So to be detail 3G referes as 3rd generation mobile telephony standard and its called UMTS.
UMTS didn't been crated for internet data transfer mainly, the target of UMTS is replacement of GSM. That means UMTS is full mobile telephony system, with possibilities to natively (w/o TCP/IP help) transfer video of caller (mainly known difference to old GSM). Data possibility of UMTS are know as HSPA and it mutations that are faster then last one ;p
http://en.wikipedia.org/wiki/Universal_Mobile_Telecommunications_System read this for more