Some people are doing a fantastic job explaining the iPhone hype, but I think there's a huge piece missing in all this analysis (otherwise, I'd stay shut-up on the exhausted matter). The iPhone is a big deal because of the Safari as the SDK announcement.
Until now, carriers ruled their devices with tyrannical control, stifling innovation at any turn. If a third-party wanted to get software on a device, they had to go through the carriers. Some software has been developed for JAVA enabled phone, possibly allowing you to by-pass the carriers, but anything that started to take business away from the carriers products ran a risk of being shut down (blocked), undoubtedly keeping many folks way clear of the phone space.
So what's the coup?
If you think Jobs had an easy time getting this device made, and that AT&T just rolled over for any request, you're out of your mind. If you need a refresher on this matter, go back and read WIRED's Battle for the Soul of the MP3 Phone, which exquisitely dissected the Rokr debacle of 2005, and the process of dealing with these hideous companies.
So, sacrifices were made in the making of this devices (Edge network, locked SIM card), but you have to believe Jobs went in fighting.
And what did he fight for?
I speculate that along the way, Jobs probably made a compromise that the device wouldn't be open to 3rd party developers (meaning AT&T would also get to okay future software placed on the phone by Apple) and Jobs said "A-O-K" to this, as long as Safari was as fully featured as possible and AT&T had no control over it.
And this was the carrier coup. For so long they've tried to control what's on the device, but a modern browser and "Web 2.0 -- web as a platform" have changed all this. Now anyone can develop for the iPhone, rather than just some, without the fear of the carrier.
If Jobs had to choose between an open phone and an open browser, then I dare say, he compromised well on this one.