Adopted Google Voice on prepaid phones as a cost-cutting measure several years back. Little more than a year ago, got a cheap Android phone and put my prepaid SIM in there. It sucked as a smartphone. Many games were missing from the market, no OS updates ever materialized, and I couldn't even buy from the market for the longest time because My "Google Apps account" wasn't a "Google account." It was, but whatever. Kindle was slow, Youtube practically unusable (wifi). Eventually frustration and envy drove me to the iPhone late kast year. And now it actually does most of the things a smartphone is meant to do.
Except phone calls. As I said, I adopted Google Voice years ago. Number porting wasn't an option when I got it so went through the pain of changing my phone number with everyone. So now I have a Google address book, using the Google Voice app. Everyone has two phone numbers, depending whether I'm calling them from the iPhone or the Google Voice app. The address book living with Google means Siri is often confused by aliases (she forgets who my wife is, or any of those sorts of relational terms).
Android was and, near as I can tell, still is a mess as compatibility goes. The Google Apps account mess was finally fixed late in my ownership, but the non-existant software updates still have no real answer. Part of me hopes Samsung or HTC forks Android to make a single, truly updatable version. Right now both platforms have a severe flaw; iPhones in that you must fully drink the koolaid, and Androids that in the name of being so open, nothing is reliable. Neither phone is perfect. iPhone is generally better, and I would rank it above the Android, but neither of them is anywhere near Fantastic.