You can for example while on 3G/EDGE/GRPS:
o Make free calls using VoIP software like Skype, Fring, Truphone and others
o Watch TV with SlingPlayer
o Watch high quality YouTube Videos, just like on WiFi
o Download apps bigger than 10MB
o Download podcasts bigger than 10MB
Developers were forced to put those restrictions in by Apple, but since with the help of 3G Unrestrictor, the apps actually "think" they are on WiFi, you can do all that.
Verified applications include: Skype, Slingplayer, YouTube, AppStore, iTunes Store, Nimbuzz, Fring, Truphone, FriendCaller, SipPhone
3G Unrestrictor supports the iPhone, iPhone 3G, and iPhone 3GS. It is now available from the Cydia Store for a cost of $2.
[Thanks to Mandeep for the vid!]