I’m just putting two and two together here, so hear me out: if an iPhone 4 can only make FaceTime calls over WIFI like the iPad 2, could an iPad 2 make a FaceTime call over 3G by connecting to an iPhone 4’s Personal Hotspot feature which is WIFI?
It’s traditionally been a loophole. Skype for Mac was able make video calls over a tethered 3G connection long before Skype for iPhone could natively do so. It’s an interesting proposition if it’s possible because it actually puts the 3G iPad 2 at a disadvantage as far as value.1
The broader question: if you have an iPhone 4, why buy a 3G iPad instead of a WIFI iPad?
By which I mean taking the money from an iPad data plan and putting it into a iPhone data sharing plan would enable FaceTime over 3G versus having separate plans which means no 3G FaceTime in addition to costing an extra $130. ↩