People forget that without Cingular there would be no iPhone. No other carrier was going to give up that much control, but Cingular was looking for an edge and took a chance. Cingular was bought by AT&T in part because of the iPhone exclusive.
Cingular has said that they didn't give up very much. After all, the biggest procedural change was that Apple wanted to handle all warranty work (easier for the carrier).
Interestingly, Verizon turned Apple down for reasons that later melted away. For instance, the biggest negative was that Apple refused to allow Verizon's sales partners such as Best Buy to carry the device. (Yet nowadays even Walmart and Radio Shack do.) Apple also wouldn't allow a direct subsidy, or carrier insurance.
What most people don't know, is that Apple did continue to approach Verizon for almost a year during 2005-6 (until they signed with Cingular). But midway the ill-fated Apple-Motorola ROKR "iTunes Phone" had come out. Yikes. Combine that with no third party apps, no GPS and no 3G, and an Apple phone would not sound too attractive.
OTOH, I betcha if Apple had ever showed a prototype to Verizon, things might've been quite different today. Consider the fact that AT&T's three year exclusive allowed Android phones years to get an unopposed foothold on all the other US carriers. Biggest goof up Apple ever did, IMO.
The word was that Apple also got a chunk of subscriber revenue, since the phone was selling at MSRP. I'm not sure if those agreements are still in place; by now they're probably gone.
Yep, what Apple got for the first iPhone was the money traditionally set aside each month to subsidize a phone. In other words, Apple was not only getting full retail price, but taking each user's subsidy as well. (AT&T didn't care, since it didn't cost them anything extra.)
Unfortunately for Apple, it wasn't long before many (20% +) iPhones were being unlocked and sold to non-AT&T users. Apple saw no monthly revenue stream from those phones.
For that and other reasons, Apple changed for subsequent iPhones to the usual subsidized sales method of getting a full large amount upfront, and letting the carriers handle the rest.