I don't want to carry an iPod Touch and a phone
I like the iOS user experience
I prefer having a smartphone that integrates all I do
Agreed. The complete integration between 2 iPhones, an iMac, and a MBP is a huge benefit. Also, I only have to carry one device.
If I were to get an iPhone, I would only pay the monthly price for the voice plan, I would not buy a data plan - I would rely on Wi-fi for that.
I think that all of the wireless companies require you to have a data plan.