T-Mobile, which has been supplying Wi-Fi services at Starbucks locations for years, has sued Starbucks over its new plan to provide Wi-Fi services delivered by AT&T at its coffeehouse locations.

T-Mobile complained that the Starbucks-AT&T agreement, announced in February, violates its deal with Starbucks. In its complaint, T-Mobile said it had the exclusive rights to "sell, market, and promote its services" in Starbucks stores until a store was converted for AT&T users. T-Mobile also said the coffee boutique chain had secretly worked with AT&T on their deal.

AT&T is gradually equipping 7,000 of its locations for Wi-Fi. Consumers are confronted with a bewildering menu of Wi-Fi services. T-Mobile continues to offer Wi-Fi services, while Starbucks is offering two hours of free AT&T-provided Wi-Fi service to consumers who purchase a Starbucks Rewards Card. AT&T also offers free services to Starbucks customers who subscribe to certain AT&T services, including broadband.

Recently, AT&T began to deploy its service in Starbucks locations, starting near its headquarters in San Antonio. The deployment switch from T-Mobile to AT&T is not expected to be particularly challenging, because the two cell phone providers utilize the same GSM-based infrastructure.

"T-Mobile had made a very significant investment in the technology and equipment necessary to provide Wi-Fi service in the many thousands of Starbucks stores in the United States," T-Mobile's complaint stated, the Reuters news service reported Monday. "Starbucks and AT&T ... secretly developed a promotional plan under which they would offer 'free' AT&T/Starbucks Wi-Fi even in stores that already offered T-Mobile infrastructure."