if you're goin from Apple to Android and you don't get a Google or unlocked phone, prepare to be restricted by carrier branding shit running in the background draining your battery. Telstra is the worst, Voda/3 is almost bad, and optus is OK. Also you don't get OS updates straight away cos it works differently:
Apple OS update process: Apple -> You (via iTunes)
Android OS update process: Google -> Manufacturer (HTC, Samsung etc who put their wrapper around Google's "vanilla" OS) -> Carrier (Telstra, Voda etc who put their wrapper on the manufacturer's wrapper) -> You
I know guys who are still running 1.6 (currently up to 2.2 with 2.3 about to come out) on their phones because the manufacturer couldn't be arsed wrapping newer versions, which means the carriers don't get shit, which means you have a slim hope in hell of gettin an update. Most people with HTC's on Optus I know had to wait 6 months after Google released their vanilla OS to get an update from Optus. This sucked cos the update included Swype which everyone was raving about when it came out... 6 months before. All cos Optus could brand the OS and put their shitty apps on it (which you can't uninstall).
Only way around it is to "root" your phone (ie jailbreak) and put a vanilla OS on it direct from google, with a couple of tweaks to make it work on your phone.
This is why carriers love the Android phones, and sell it much cheaper and push it harder than the iPhone (which Apple pushes for them).
iPhone = sell your soul to Apple
Android = sell your soul to mobile carrier