I asked the question about the swappability of the AT&T iPhone SIM and haven't seen the answer anywhere, until now. I just read through the iPhone Launch Guide found on The Boy Genius Report and on page 31 of 65 it states that MEdiaNet will be used to access the internet if a customer takes out the iPhone SIM and puts it into another AT&T device. That does it, I will now finalize my purchase strategy and get in line with all the other iPhone fans to try to secure a device tomorrow. As a reviewer, I need the flexibility to swap my SIM into unlocked devices and now that I know this is possible the risk associated with the iPhone is significantly reduced for me. I know that many other features found on other devices are missing from the iPhone, but I want to at least try the experience out for 14 days and if it turns out I like it then I can switch at least my wireless data access to AT&T and sell the iPhone.
Also, the document states that MMS and IM messages are included in the customer's iPhone Data Plan so even though this functionality doesn't work on the iPhone itself you will be able to use it with other devices when the iPhone SIM is popped into it. Cool!