The conversation was actually pretty interesting. I told the rep I had pulled my SIM card from my iPhone to use it in my old RAZR (I actually did have a RAZR before I got my first iPhone) and that on the RAZR I could not send MMS. He did some research and said that the SIM card I have was made for the iPhone and wouldnt allow me to send MMS through another phone. He also said I could go to an AT&T store and get a SIM card that would work with BOTH my iPhone and my RAZR and it would allow me to send MMS on the RAZR, and that the card swap would be FREE.

I am yet to do this (I might) but if anyone else wants to try please let me know how it goes. If you do swap your SIM card, does it still work in your iPhone? Can you now send MMS on a different phone (RAZR in my case)? Can you now send MMS on your iPhone (assuming you did the little ‘hack’ that is supposed to let you)? Or is all of what the rep said BS and you already have MMS working on your iPhone?

I did the hack and tethering works fine, and I have the icon to send pictures, and my iPhone attempts to do so, but fails at the last second and gives me a little red (!) icon.

EDIT:
Just so people stop asking, the sim card is NOT the problem. An AT&T representative was naive enough to tell me that while I was trying to enable MMS on my iPhone. Think about it, if the sim card is the problem, that means anyone with an iPhone has to go into AT&T to have their sim card exchanged to make MMS work once AT&T is ready to allow it. That would be a large irritation and waste of time and resources for AT&T (they would be throwing away a lot of old sim cards).