I hear about 3G in iPhone ads, what is that?

With 3G  you are able to download large files and access multimedia services like video on your mobile devices faster than ever before.  3G refers to the third generation of mobile phone networks that offers high-speed Internet access and video telephony.  3G brings the same super-fast broadband speeds to mobile phones that you can get at home with cable or DSL, at speeds up to 14.4Mbits per second on the downlink and 5.8Mbits per second on the uplink.