Yes, the iPhone does have a SIM, which you can move to any other ATT or unlocked phone and you get voice, texts and data (I tried it with a friend's iphone). It has also been reported on MacRumors and HowardForums that you can use any non prepaid ATT SIM in the iPhone, but you need to "activate" it (via iTunes), which means that it adds the $20 iphone data plan to whatever ATT plan you had on the SIM. I could find no info on whether the iphone plan is in addition or substitutes for any data plan currently on your account.
What I would like to learn is what happens if you try to add a blackberry data plan to an iPhone SIM or an iphone data plan to a blackberry ATT SIM. If that is possible and the two don't interfere, then the SIM should be usable in both the iPhone and the blackberry. You should get calls and texts in whatever device the SIM is in, email sent to
whenever the SIM goes into the blackberry, and pull email from the iPhone. Now, yahoo reportedly pushes email on the iphone, so I wonder what happens if the same yahoo account is pushed to both the blackberry (via BIS) and to the iphone. I would try all this, but my blackberry is on TMobile...
I didn't originally post in "other devices" section because this is a general ATT Blackberry plan question... I think there used to be a GSM Service providers section, but couldn't find it...
Incidentally, my 3 cents on the iPhone:
1. To my great surprise, the keyboard was a non-issue for me. For all my being used to tactile feedback, the visual feedback provided by the iPhone works. I was typing with two thumbs at 90% of Blackberry speed after 10 min.
2. The iPhone is significantly larger than the Pearl. If you don't need the bigger screen (for web browsing, photos, videos), the Pearl form factor still carries the day for me.
3. For corporate users, the iPhone doesn't come close to BB's security, and thus is unlikely to penetrate that market even after it offers push email, exchange integration etc.