AT&T says it will launch the eagerly-awaited iPhone multimedia messaging service on September 25.

According to AT&T, the carrier had to work on its network architecture for the past several months to handle the “expected record volumes of MMS traffic” generated by the service. AT&T will enable the service on the iPhone 3G and 3GS through a software update on launch day.

Wireless use on AT&T’s network has grown an average of 350 percent year-over-year for the past two years, and is projected to continue at a rapid pace in 2009 and beyond, said the carrier.