iPhone, let me tell you why.
Everyone has an iPod correct? If not they have some sort of Mp3 Player. Unless you are poor or don't care about music then you have around or more then 1gb. Also everyone has a phone. Some people pay as much as $600 for a phone with not even half the iPhone's functionality. (i.e. Blackberry). So their Windows Mobile Phones? The SDK for iPhone coming out will completely sync with the .NET framework and windows email servers.
So if your going to buy a $250 iPod and a $150-$300 dollar phone, just get the iPhone. My mom has 1, and it completely fucking owns. If I had the money for a data plan ($30 extra a month per person) I would get one.
Also, if you don't have a data plan (Wireless/Mobile Internet), don't bother getting anything over $150. This includes an iPhone. Without internet on the iPhone its just a phone with an iPod. But worse. Forget the WiFi, if you don't have a data plan it is NOT worth it.