Microsoft

(MSFT) - Get Report

said Thursday that it would team with

British Telecommunications

(BTY)

and

AT&T

(T) - Get Report

to offer worldwide mobile multimedia service through wireless devices over high-speed networks.

The companies did not disclose the financial details of the union.

The mobile service will be based on Microsoft's technology and deployed over the existing and planned high-speed wireless data networks. It will enable its customers to use their wireless devices for email and electronic calendars on the go, but on a wider scale than currently available through other networks.

Individual subscribers in the consumer market will be able to play interactive games, read electronic books and listen to music over the widespread high-speed network.

The companies expect to roll out the new products after testing them this fall.

Microsoft said their technology supports open standards so that application developers will be able to build additional applications.

This partnership extends the existing relationship between British Telecom and Microsoft into the broadband mobile arena. British Telecom and Microsoft had already announced they are developing corporate and consumer mobile applications for use on existing mobile networks.

The deal also builds on

Advance

, an alliance between British Telecom and AT&T that is aimed at creating seamless mobile communications services around the world.

Shares of the three companies had not changed significantly in early trading. Microsoft was down 5/16, or 1%, to 106 15/16. British Telecom was down 7 3/8, or 4%, to 188 1/2 and AT&T was up 3/8 or 1% at 60 5/8. (Microsoft closed down 3 1/2, or 3%, at 103 3/8. British Telecom closed down 9 1/4, or 5%, at 187 3/4 and AT&T closed down 2 1/2, or 4%, at 57 3/4).