I use 18866.
I dial 18866 - then the number I'm after. There is always 3p connection charge then the call is free to landlines even during the day. Mobile calls are 12p/minute, and foreign calls are cheap too.
It very reassuring, at the start of each call a nice lady says 'Zero pence per minute'. The only proviso is that you pay your bill over the internet, mine is usually about £2.50 per month.
http://www.call18866.co.uk
Have got skype too and it's great but I don't always want to stay at the PC , using 18866 means I can move around while I'm on the phone.
Has anyone got a phone that you can walk around with that is Skype enabled? Now that would be something.
ZW