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.
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.