According to AT&T's latest iPhone 3G S FAQ (PDF), the company will offer MMS messages free with a text-messaging plan at some point later this summer. Until now, some current customers have feared having to pay an additional fee for texting. Considering all the , this is probably a strategic decision on AT&T's part.
Why all the fuss about MMS, especially given that you can replicate the functionality of MMS using e-mail much more easily on a smartphone? Even if e-mail is easy for you, your friends without a smartphone have only MMS for photos and videos between phones. AT&T's support of MMS to the iPhone bridges this gap.