My agency has represented Boingo for 18 months or so now, and long before that I was a Boingo customer, a happy customer, who found that using it on my Nokia N & E Series devices and my laptops was always something that allowed for easy connectivity.
One of the missing pieces, more due to RIM's SDK, was Boingo on the Blackberry. As a Blackberry user with T-Mobile I've always enjoyed logging on to WiFi at home (via Hotspot @ HOME) or at a T-Mobile Hotspot, and having my mobile number from the USA anywhere in the world accessible to me.
That worked great in the past at places like Starbucks, some airport lounges like those from American Airlines and at some airports. But as T-Mobile has been exiting the WiFi world in dribs and drabs, the most reliable and broadest reaching aggregator has been Boingo. Now, with Boingo on the Blackberry, UMA Voice will work as well on the Blackberry as client Truphone does on my iPhone, iPod Touch and Nokia E71 virtually anywhere Boingo connects.
This is a huge step forward as the business market end user which needs connectivity now can get connectivity in more places, where T-Mobile's footprint doesn't go. With Boingo, as with WiFi of your own or within the enterprise or campus, means you can get connectivity for voice coverage higher up or farther away. Currently, AT&T in the USA doesn't have a VoIP client for their users, nor is there one with Verizon or Sprint on the Blackberry's that has any traction, as access to the SIP and WiFi stacks on the RIM devices has never been really offered.
Blackberry users though should not just take my word for it, or the insight above that I've linked to. They should also read some of the insider's viewpoints as well.