By Sam Oliver

Published: 08:30 PM EST

American iPhone users should see multimedia messaging features unlocked late in the morning Friday on the west coast by way of a carrier update file that will be delivered through iTunes, AT&T announced Wednesday.

"MMS Update: We know you’ve been eager for this service so we wanted to offer a quick update on the launch plans for MMS on Friday, Sept. 25," AT&T wrote on its official Facebook page. "Late morning, Pacific Time, on Friday, the new carrier settings update enabling MMS should be live and ready to download through iTunes. We’ll provide the steps and all of the details you need right here at that time."

That means east coast residents will likely see their update available sometime early Friday afternoon. It also confirms that an iTunes update to the phone's carrier profile will be necessary for MMS to be activated.

AT&T "very nervous"

A note published by DSLReports cited a source familiar with the company's MMS upgrade as saying, "Starting at 10AM Eastern (on the 25), AT&T will send out a mass text to a group of iPhone users telling them that MMS now works on their phone.

Assuming all goes well, "They will keep doing groups of phones on the hour throughout the day," the source said. Official word from company spokesman Seth Bloom said the upgrade would be targeted at early afternoon on the East Coast, or late morning for users on Pacific Time.

The source said AT&T was "very nervous" about the launch, due to seeing a surge in traffic from just a limited number of iPhone users selected to participate in advanced testing of the new service.

Working to keep up

Apple added MMS features to the iPhone as part of the 3.0 firmware update in July, but AT&T acted to opt iPhone users out of the service because it could not accommodate the anticipated demand it predicted iPhone users would require.

MMS allows users to send graphics, audio clips, location and contact files, and even video clips via an SMS-like messaging system. The new MMS features require an iPhone 3G or iPhone 3GS.

Weeks ago, AT&T announced that MMS would be available for the iPhone 3GS and iPhone 3G, but not the original iPhone, on Sept. 25. Tuesday, the nation's second-largest wireless carrier began sending out text messages to customers informing them of the upcoming change.

Picture and video messaging was originally scheduled to arrive in the summer, but will be a few days late. AT&T has said that iPhone data usage has been very taxing on its network, leading to delays as the company attempts to strengthen its service.

Originally, iPhone tethering was also announced for the summer, but AT&T officials have said that service is coming at a later date, with no specifics given. The company apparently has no intentions to cap bandwidth for iPhone users.