The system, which bears the project name Enterprise Fixed-Mobile Convergence and is expected to go live early next year, will allow corporate users to have a single mobile device they can use over WiFi in the office, at home or in hotspots, and as a regular cellular wherever a wireless LAN connection is not available.

The London-based carrier, which serves corporate customers internationally via a global MPLS network, has been developing fixed-mobile convergence offerings for a couple of years, having launched its BT Fusion service for consumers and small businesses in the UK last July.

That service, which currently has some 13,000 subscribers, uses Unlicensed Mobile Access technology to encapsulate circuit-switched GSM traffic for transmission over a fixed-line network, initially using a Bluetooth connection to a DSL router and now transitioning to WiFi.

Fusion charges users at fixed-line rates when they are in or around the home, and mobile rates (via an MVNO service on the Vodafone network) when outside.

For its enterprise offering, on the other hand, BT wants to use 21st Century Network (21CN), the end-to-end IP infrastructure it is installing between now and 2008, and for this reason it has chosen Alcatel to lead-manage the implementation of Enterprise FMC.

The Paris-based telecoms equipment provider will design, integrate and test the system, and will also supply key platform elements from its Managed Communication Services portfolio to ensure that the system integrates seamlessly into BT’s enterprise customer sites. Lucent Technologies is expected to provide its VPN Firewall and VitalAAA security products and design team specialists.

In particular, Alcatel will supply its Corporate Mobility Manager, a component of its Intelligent Mobile Routing portfolio, which will enable BT to offer an entirely SIP-based FMC offering on 21CN rather than the UMA technology that underpins Fusion. Thus the handsets Enterprise FMC customers will use will only require a SIP client and WiFi radios in addition to cellular ones, whereas Fusion requires UMA-specific clients.

This in turn should enable corporate customers to choose from a wider range of dual-mode devices. The IP basis of 21CN, with an IP Multimedia Subsystem in its core, will allow corporate users equipped with such phones to use office phone features that currently require a PBX, such as conferencing, call-forwarding, and diverting calls to team members when in meetings.

BT is pushing the cost-saving aspects of the device, as all mobile calls between internal users using the wi-fi connections on the handsets will be free if the employee is on a company’s premises. This includes calls made between corporate sites and, potentially, across international offices. Money will also be saved when connecting outside calls to a corporate mobile. This is because BT’s new network technology can deliver a call directly to the new handsets.

Among the aspects of the service still to be determined is the provider of international cellular connectivity. At the moment the MVNO relationship with Vodafone is specific to the UK, and it is an open question whether BT will seek to expand that deal to Vodafone’s other properties around the world.

When BT announced plans for an FMC offering for businesses in Spain this year it said it would consider all three of the country’s mobile operators as potential partners and it is known to be seeking MVNO status there now that the Spanish government seeks to force the carriers to entertain potential partners.

In the US, Vodafone has a minority stake in Verizon Wireless, with the majority held by Verizon Communications, which is a direct rival of BT’s in the market for corporate connectivity/WAN services, which would seem to make it an unlikely partner in any Enterprise FMC service from BT. Earlier this year the British group’s US arm BT Infonet said the company could look at WiMAX as a means of providing wide-area wireless connectivity in that geography.