If they didn't give Cingular exclusive rights to the phone, then the iPhone wouldn't be at all. As it is now, carriers dictate exactly what manufacturers can put in their phones. Cingular was the ONLY one that would give Apple "special treatment" and allow Apple full reign on their design - most cell phone makers have to follow VERY strict guidelines.
Not here they don't. If a carrier decided to cripple a phone's functionality or alter it in any way from the manufacturer's specs they'd be run out of town. Same if they tried to make people pay to receive calls - now that's just plain stupid.