On my BT Infinity service (just recently installed) It appears that FON users get 10Meg down and 250kbps upload available to them. Bit more speedy than 512kbps

Telcon,
I've been using Fon successfully on my iPhone for 2+ years.
I use it by:
1) Ensuring the phone connects to the Fon wireless (Setting ->WiFi-> Connect to one labelled Fon)/ or BTOpenzone (in UK) if Fon not displayed

2) Opening up the Safari browser - it will take you to a logon page

3) Log on as a BT Totalbroadband user using your Broadband id and password.

I haven't used the app yet but the above has worked well for me in the UK, Italy, France and Spain on both iPhone and iPad.

The only confusion is that overseas BT Openzone areas (e.g. in airport etc) often don't give Fon access.

To make the whole procedure easier a wifi 'sniffer' app is also worth buying (<£1).

Happy surfing
jawdrops