There are certain basic functions that many of us find ourselves without that prevent the iPhone from being a complete device. For me, it is a functional calculator that I can use without a network connection. There is a bookmarklet version that is almost viable, but painful to use. The lack of this basic (for me) functionality necessitates me to bring my big ass HP 50G with me. Sometimes I just need a square root... sometimes a cosine... but without these I have to guess at the numbers. Sad, seeing as I have a little computer in my pocket that could easily process the information.
Unlocking is a different story than 3rd party apps. There are specific situations where I can understand people wanting to be able to pop in a T-Mobile SIM card in the US where it doesn't hurt AT&T and Apple through their agreement. These are pretty rare, but they do exist. Consumer preference doesn't count on this one...
But, for people that travel internationally, the picture is much different. Roaming rates are absurd, especially for data. Purchasing a local pre-paid SIM is the only viable way to stay in touch when abroad. Having to buy an extra phone that works on the local network is an insult... especially when that substitute phone can't match the functionality of the phone you already own.
([RANT]I paid a lot of money for an international roaming plan for my Blackberry that didn't work. When it didn't work, Cingular wasn't working to help me out-- I would spend hours with no resolution on the phone. The solution to my problems was simple... let me use a local SIM card. This was impossible for them to permit though; even though they would let me unlock the phone, I needed a blackberry plan on my SIM for the phone to be functional for any data services. This is what has made me want to desperately avoid a blackberry for years, and I thought the iPhone would be my salvation. The reality is that is just isn't as well executed of a lock-in plan...[/RANT])
Apple and AT&T need to get with the current century and stop trying to lock their customers into services they can't provide.