Mark, totally agree with the 3 phases. Would also like to add that in Phase 3 the devices that really enabled usage of 3G also showed up (iPhones and also USB dongles etc.). As a result in phase 3 the world moved beyond the health club model of selling data plans - where most people (were like me) they bought health club plans but did not really use them regularly, because it was just too painful to actually use. With improvement in UI, that has changed for wireless data. This is exposing the coverage and speed gaps etc. you mention. I wish the same change can be made for excersing more user friendly. 
My opinon based all the numbers I have seen, is that most of the usage comes from laptops/netbooks (surprisingly its is not the iPhone). These devices have WiFi in them too and the usage is typically nomadic. All this argues for WiFi adoption.
However there is one problem that needs to be solved (at least on the network side) - WiFi has a million managers. This makes the experience painful and while this can be fixed with a AAA server there are very few WiFi operators with scale. This cripples usefulness of cellular service provider offerings around WiFi. The primary benefit of cellular is the fact that it simply works everywhere and does not require at a minimum inquire about the local IT policy and maybe fork out a few dollars every time he/she connects to a different network.
