The easy access to voice mail that AT&T and T-Mobile offer their mobile phone subscribers when abroad infringes patents held by a Swiss company, a lawsuit filed in federal court in Delaware says.

Starhome GmbH of Zurich filed a lawsuit last week seeking to prevent AT&T Mobility LLC of Atlanta and T-Mobile USA Inc of Bellevue, Washington, from offering some international roaming services and asked the court to award unspecified damages.

AT&T Mobility is a subsidiary of AT&T Inc and T-Mobile USA Inc is a U.S. subsidiary of Deutsche Telekom AG of Germany.

The May 25 lawsuit was also brought against Roamware Inc of San Jose, California.

Starhome develops products to improve international mobile phone roaming and supplies 178 cellphone companies worldwide, according to court documents.

The lawsuit stems from two patents issued to Starhome in 2005 and 2007.

The patents cover services that allow mobile phone subscribers to use the same short codes they use at home to access voicemail and other services when abroad without having to dial long international calling codes, according to court documents.

The patented services also allow airlines and car rental companies to offer customers access to local toll-free numbers when overseas.

Shares of AT&T were 1.3 percent higher at $24.64 in afternoon trading on the New York Stock Exchange. Shares of Deutsche Telekom ended up about 1 percent at 9.23 euros in Frankfurt.

AT&T and Deutsche Telekom declined to comment. Roamware did not immediately reply to requests for comment.

(Reporting by Tom Hals; Additional reporting by Nicola Leske in Frankfurt; Editing by Steve Orlofsky and Gerald E. McCormick)

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