In an effort to show wide support for its newest Windows Mobile operating system, Microsoft is highlighting several announcements from handset makers at the 3GSM telecoms conference Barcelona.

Device manufacturers including Toshiba and LG Electronics are announcing plans to offer phones based on the new Windows Mobile 6.0.

Some operators are also allowing customers to upgrade from the previous Windows Mobile software. T-Mobile US, for example, announced it will offer an upgrade to the new operating system to customers who are using its HTC device running Windows Mobile 5.0.

Most of the phones running Windows Mobile 6.0 will become available in March or April.

Analysts and competitors have criticised the Windows Mobile platform for being available on a smaller range of phones than other operating systems, specifically Nokia's Symbian S60. But Microsoft argues that it is offering the best choice to users.

"We are now promoting 140 different form factors from 48 device makers," said Marianne Roling, director of mobile embedded devices for Microsoft Europe, Middle East and Africa.

BT said it is taking advantage of Windows Mobile 6.0's built-in voice over internet protocol (VoIP) capabilities by selling an HP device running the software to customers of its converged Fusion service.

The HP iPaq 514 running Windows Mobile 6.0 will be offered to business users of the service, which lets customers make low-cost VoIP-over-Wi-Fi calls as well as standard mobile calls. Users can roam between the two networks without dropping calls.

Windows Mobile 6.0 includes support for wireless VOIP but users need to subscribe to a service like BT's Fusion in order to seamlessly move between the networks, Roling said.

Microsoft also announced that The Carphone Warehouse will offer a hosted mobile email service to small and medium-size businesses based on a hosted server product from Microsoft. End users, who can use Windows Mobile 6.0 phones, will pay a monthly fee for the service.