The iPad 2 wifi only model works great with Facetime. I'm pretty sure with both iPhones and iPads that wifi means wifi by means of DSL or cable and that you won't be able to communicate via a cellular connection even if you wifi connect wirelessly to another cellular hotspot device. It has nothing to do with speeds as my former DSL wifi at home was often as slow as my old iPhone 3G. I think it has a lot more to do with the cellular traffic and if it was cellular enabled there would be an explosion of Facetime talk that the networks could not handle. Besides, even if you could establish a connection through a hotspot setup you would burn through your gigabyte allowance in no time.
Like I said I have the unlimited data plan on my Droid X but I don't have a front camera so when we get the Ipad2 we plan on using public wifi and Facetime to see the grandkids...when I get a new phone we will use Tango video calls to see and talk to the grandkids as I probably won't be purchasing an Iphone...
I've been to a lot of campgrounds where they've disabled video on their wifi so you can't use services like Netflix and YouTube. Having never tried Facetime at them I don't know if that would have been included. We've only used Facetime via our home wifi. Public wifi at places like McDonalds and Starbucks have been anywhere from bad to good, but this past year was much better on the average than the previous year. I always check Speedtest.net to see and predict what I can accomplish on a public wifi connection.
That Tango Video looks interesting.
2011 Great West Van Legend Sprinter B Camper Van
Visited states in an RV