I'm a Fonero, but I have to admit that's only because I was lucky enough to get in on one of Fon's occasional promos, where if an existing user recommended you, you got an AP for free.
(The current deal isn't bad, by the way - get a recommendation and the AP costs you just €/$20.)
The one snag I've found is that Foneros don't always place their APs in positions that give good coverage to visitors - plus of course they're more often in residential districts which don't get many tourists. More than once I've found myself standing on a cold street corner in a strange city, trying to get a signal from some distant 3rd floor apartment! On the other hand, most times it has worked....
I freely admit to being (a bit of) a geek, so I've positioned my Fon AP upstairs at the front of the house, where it has line of sight to the pub over the road. Signal strength over there isn't as high as I'd like, but it's just about enough - it's probably also where my very few visiting users connect from.
Maybe I should get the high-gain antenna, but even so, it would be nice if Fon gave its users a bit more advice on how to locate their APs for best coverage. Back to the question thought - what does the BT deal mean for Fon in the UK?
I've just done a quick survey of a few hundred yards of road in West London (using my Palm TX with WiFi-Where) and found 40 APs, of which nine advertised themselves as BT Home Hubs. There was only one Fon ID though - mine - so BT is obviously not in a hurry to roll this out.
Still, if even one or two in every ten BT broadband customers also joins Fon, that's pretty good coverage. And of course, for them it's free - it's just a firmware update for their Home Hub so there's no need for an extra AP.
We just need BT to roll out that firmware a bit faster.