I'm not sure I totally agree. Not that Truphone doesn't have a great service, but ultimately UMA plays (and indeed, all alternate wireless services) are about price. We seek to use WiFi hotspots because they're cheaper.
Nope, I actually think that another of Andy's clients, Mobivox, may be just as big a play. Mobivox offers local dial access numbers in 35+ countries. When you call the number, you speak with an IVR (the lovely VoxGirl), who then routes your calls at VoIP-alicious prices to wherever you want. All from your mobile handset… or if you prefer, from a wireline handset. Calls between Mobivox subscribers are free. Calls from Mobivox to Skype are free as well.
Why is this better than WiFi? One word. Ubiquity. Like it or not, WiFi networks aren't everywhere, and cellular networks are. With smart use of mobile pricing plans, you can basically call anyone you want for next to nothing. For example, here in Canada I pay $15/month for Rogers MyFive, which allows me an unlimited number of calls and text messages to and from any of five numbers on any networks. T-Mobile has a similar program in the US called MyFaves. So I set my MobiVox local access number as one of my five. Next I loaded my entire address book into the MobiVox system (note… it's still beta and it's very slow with 2000+ address book entries). Now I can call anywhere in North America from my cellular phone for 1.9 cents per minute, and no airtime charge.
When I compare Truphone to Mobivox, here's where I end up. Truphone calls are free, from WiFi hotspots. Outside a hotspot, I pay normal airtime charges. MobiVox costs me 1.9 cents a minute, except between Mobivox subscribers. Whether Truphone or Mobivox is better for you will totally depend on the kind of mobile user you are. If you're on the road all the time, Mobivox is the best choice. If you're one of those people who makes a lot of cellular calls from the office, then Truphone is the better choice. However you do the math, though, consumers come up the winner.