Apple and AT&T have been slapped with a lawsuit by a consumer for the third time in less than a month, over alleged deceptive trade practices and breach of contract relating to befooling people to believe that multimedia messaging, or MMS, was already available on the iPhone.

Apple and AT&T announced on June 8, during Apple’s Worldwide Developers Conference keynote that MMS would not be available until later in the summer.

The plaintiff, Deborah Carr, from Ohia, has alleged that millions of customers fell for the deceptive representations by Apple and AT&T and bought the 3G and 3GS to experience MMS application in June this year.

The MMS failed to work even after downloading the new 3.0 Software Update application, said Carr.

Two similar cases, one in Illinois and another in Louisiana were also filed against the companies in August.

In principle, Apple has enabled MMS in iPhone OS 3.0, with 29 carriers across the world having activated MMS on their iPhone with the launch of the application on June 17. But the application remains missing in the United States as AT&T still remains unready to activate it, revealed the company on June 8.