I probably ought not to say this, but anyone with a BT line should get TalkTalk as their call provider ASAP. They are brilliant, simple to understand, and everything is done smoothly and professionally with absolutely no hassle.
http://www.talktalk.co.uk
I have an ntl line AND a BT line, for mainly historical reasons. Allows me to shop around very nicely for the cheapest deals on call charges.