Localphone have introduced a callback service. Handy if your on a expensive payg tariff.

To quote them "Perfect for pre-paid (PAYG) mobile customers Call our Callback number for free and avoid paying your operator anything"

http://www.localphone.com/services/callback

They call both you and your contact number  so you’ll pay  lower rates for both parts of the call.

E.g. If your on a UK Payg Mobile calling another UK Mobile  you’ll pay 1.8p + 1.8p = 3.16p a minute   . No connection charges. Cost of call calculation will be based on the length of the call rounded up to the next nearest full minute.Its a Prepay Service.You agree that Localphone can expire any credit that remains unused for a rolling period of 365 days (if you do not make a call for 365 days the credit will expire).

Can also be used from contract phones eg if you run out of inclusive minutes. ;)