BT Internet Option 4 is now available for £23.99 a month for the first 3 months and £29.99 thereafter (18 month contract) for new users, thats just an extra £5 per month for existing Option 3 (ie unlimited) users.
You get a snazzy new mobile thats great for Internet, email, etc and has a camera etc. It comes with 50 minutes talk time and 50 free texts per month and 10Mb monthly download allowance for when away from an access point. Think BT uses the Vodaphone network and the phone runs on Windows Mobile 6, mine was delivered very quickly!
Whilst within reach of your BT HomeHub you can download and browse to your hearts content for nowt, including "free" calls over BT Talk. In any BT Openzone you have 500 minutes access per month, and soon (if not already) free access via any BT FON point.
"The brand new BT ToGo is a phone that comes with BT Total Broadband Anywhere as standard and is worth £150. The BT ToGo lets you check your emails, surf the internet and make calls when you're out and about."
Away from home standard-ish bt mobile prices apply (see link in 2nd reply below)