T-Mobile makes fixed/mobile convergence real

Unlimited HotSpot Calling ensures that you won't miss that important call

There are so many reasons I don't send good enterprise handsets back after their review periods expire. Often, seemingly small things that aren't important enough to warrant special attention during a two-week eval pop up later when I'm out and about with the device. Take T-Mobile's Unlimited HotSpot Calling, for example. T-Mobile configured my loaner SIM card with this service add-on that gives me the ability to use UMA (unlicensed mobile access) handsets to make voice calls from T-Mobile HotSpot locations. Unlimited HotSpot Calling seems an esoteric item for two reasons: In the United States, T-Mobile's selection of UMA-enabled handsets is paltry (models that are practical for professionals count exactly one), and really, how often are you camped out in a T-Mobile HotSpot thinking, "Gee, I wish I could gab on my cell all day for free"?

That's one perspective. The other is that UMA is key to the success of fixed/mobile convergence (FMC), which allows enterprise employees to roam around a corporate campus using their cellular handsets like portable desk phones and to have calls made to their desks find them in the car, at home, and on the road. If T-Mobile's Unlimited HotSpot Calling works, then the ingredients for FMC are in place.

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It works. A couple of days ago, I was at the airport, in the bowels of baggage claim, when my handset du jour, a T-Mobile BlackBerry Curve 8900, rang. It's never done that before. Bag claim at this airport is so thoroughly insulated against cellular signals that you'd think the architect had that feature in mind. If a phone can see a cell tower at all from down there, a single bar winks feebly in the mobile's display. Occasionally SMS can squeak through that link at teletype speed, but voice doesn't stand a chance. This time, the caller's voice boomed through as if I climbed the tower.

When I checked, the Curve 8900's display had a "UMA" banner, indicating that my phone was operating through the airport's T-Mobile HotSpot service. My call, instead of weakly winding its way to the nearest tower through the thick concrete walls and radio-rich airspace, was being passed over an IPsec tunnel to a gateway on T-Mobile's network. It's not VoIP as we know it, but more like GSM over IP. UMA-equipped handsets will hop from Wi-Fi to cellular and back, even during a call, with complete transparency to the user. To T-Mobile's cell network, the HotSpot router at the airport is just part of the infrastructure. Wi-Fi/GSM hand-off works the same way that ordinary cell tower hand-off does.

One number hunts you down
I can't get excited about VoIP for business no matter how cleverly it's packaged, but UMA grabs me because, as the song goes, it's one less bell to answer. I would love to deploy a fleet of UMA handsets in lieu of desk phones. With UMA, everyone gets exactly one phone number. All of the calls they make, whether cellular or Wi-Fi, would bear the company's caller ID, and I could provision and manage phones from the operator's Web interface. If there were coverage dead spots on campus, I could fix them by rolling out additional UMA-equipped routers. Ideally, I could send telecommuters home with routers that extend Wi-Fi calling to their house. It's all flat rate -- no airtime charges apply to Wi-Fi calls -- and there is zero configuration. I'd handle provisioning of UMA phones or network devices by inserting a SIM card. I'm all about being able to manage my own phones and infrastructure.

I've worked with T-Mobile's UMA implementation before. I have a T-Mobile@Home Wi-Fi router that, until recently, provided me with UMA services in my office. This stopped working when T-Mobile recently deactivated the SIM it had loaned to me, but apparently T-Mobile added Unlimited HotSpot Calling to my plan when it turned my service back on. It's odd that I can now make free unlimited Wi-Fi calls from coffee shops and airports, but not from my desk, when before, the reverse was true.

As appealing as it is, UMA is one of T-Mobile's most poorly marketed services: Type "UMA" into the search box at T-Mobile's Web site and you get zero matches. The fact that the service has such a low profile left me wondering about T-Mobile's commitment to UMA, but the operator just brought a new offering, Wi-Fi Calling for Business, to the U.S. market. Targeted at businesses with at least 100 lines, the new service offers unlimited Wi-Fi calling via T-Mobile HotSpots and private Wi-Fi networks at a fixed contract price. The shape of your workforce determines the value of UMA services.

The savings kick in only when you're on Wi-Fi, and it's the phone, not the user, that picks the network. If an admin changes Wi-Fi credentials such that UMA phones can't log in, even in-building calls will be routed through the cellular network and they'll start eating daytime minutes, an expensive mistake that might not surface until the next phone bill. But look at it this way: At least the calls get through. If infrastructure glitches knock VoIP devices off-line, they don't have T-Mobile's cellular network as a backup. In business, what's often most important is that customers and clients be spared inconvenience. Problems with my phone system, especially those caused indirectly by my network infrastructure, shouldn't cost me business. UMA's inherent network redundancy, along with the simplicity of assigning a single "follow me" number to each worker without PBX routing or forwarding, puts it at the top of my list for fixed/mobile convergence.