Thank goodness Apple made the right choice on this one. In all price plans available for a new iPhone, the data usage is unlimited. The data price for the iPhone was crucial; a device so dependent on data had to offer a data price plan that was reasonable. There’d have been outcry if restrictive data plans forced users to keep a constant eye on how much they were downloading.
You can also activate your iPhone from home, using functionality built into iTunes; annoying iPhone guy tells you how in this video. You’ll need OS X 10.4.10; and you have to sign small print agreements with both Apple and AT&T. Quite what’s in those agreements, we can’t tell you just yet. Be interesting to find out, though.