One of the hotter convergence topics of late is fixed/mobile convergence - the ability to merge wired and wireless telecom resources so that users can have what amounts to their desktop phone in a handheld device in their pocket.

It sounds like a simple concept, but FMC requires lots of technical stitching on the part of the carrier or vendor to smooth out the seams between the wired and unwired worlds. There are multiple instantiations of FMC from which an enterprise can choose, which makes the right FMC decision more difficult.

But once the networks are stitched and the decisions about whether to opt for a carrier managed service or enterprise-centric FMC implementation are made, the benefits are manifold, industry experts say. They include the ability to be reached through one phone number wherever you are - at your desk, around campus, roaming about or at home - as well as reduced enterprise telecom costs by, for example, bypassing international mobile roaming charges when making cross-border calls.

The end game with FMC, observers say, is to equip workers with what amounts to the enterprise PBX in their pocket.

“It’s mostly field workers needing access back into their office,” says Craig Mathias, founder of mobile and wireless consultancy Farpoint Group.

Another driver is cost, Mathias says. FMC melds several disparate infrastructures - such as TDM and packet VoIP, IP data, Wi-Fi and various flavors of cellular - into one. A single infrastructure is a lot less expensive to operate than several.

Enterprises also can save on telecom costs. In addition to bypassing international roaming charges, businesses can tame their out-of-control cellular bills by selecting one or two service providers or vendors to include cellular as a component of an overall FMC or unified communications package, Mathias says.

But this is all promise; FMC is a nascent market and there are few implementations today.

Though FMC registers barely a blip on the radar screen, there will be 92 million FMC subscribers worldwide by 2011 and FMC revenue will amount to $28 billion by that time, representing 3% of overall mobile subscriptions globally, according to market research firm Informa Telecoms & Media. The firm says the United States will lead the way with 33.2 million subscribers.