Apple let down iPhone watchers and owners when it announced in June that iPhone 3.0 software would support MMS but implied that AT&T would not yet allow it. The service launch was delayed several times, with exclusive carrier AT&T citing the need to make sure its network was ready. The feature will finally become generally available on AT&T iPhones on Friday when iTunes delivers a carrier settings update for the wildly popular phone. The carrier has said it expects "record volumes" of MMS traffic after the launch. MMS lets people send pictures, audio recordings, video clips or contact information along with an SMS (Short Message Service) message.

However, the service in question has been out for years on other handsets and hasn't exactly taken the mobile world by storm. In 2008, MMS made up just 2.5 percent of all messages sent from phones worldwide, meaning about 97.5 percent were SMS text messages, according to ABI Research. ABI expects the MMS share to grow to just 4.5 percent by 2014.

Given the amount of data that iPhone fans are already using on AT&T's network, for Web browsing, video, e-mail and social networking, it would take quite a popularity breakthrough for MMS to drag down the infrastructure through sheer traffic, analysts said. However, the carrier's fears in one respect may have been justified, said ABI analyst Dan Shey.

Several factors have dampened the popularity of MMS, according to analysts and industry observers. A big one is that the messages still don't always get through.

"Interoperability between carriers has always been an issue, and that's why MMS usage hasn't really taken off," Shey said. Delivering multimedia content from one phone and one network to another can be complicated with photos and gets even more involved when it comes to video, with large file sizes and multiple available formats, he said. What's attached in an MMS, 98 percent of the time, is just a picture, he said.

Another problem has been the complicated user interfaces on some phones and networks, which at times have forced senders to go through several steps to attach their content and recipients to go to a link within an SMS and provide a password along the way. The iPhone streamlines this process for iPhone users but not necessarily for the recipients of their messages.