Gradwell are also 3p for 0845 and 7p for 0870.
http://www.gradwell.co.uk/voip/callcharges/
BT standard charges are:
0845: 3.95p daytime, 1.00p evenings and weekends
0870: 7.91p daytime, 3.95p evenings and 1.50 weekends
http://www.productsandservices.bt.co...ialisedNos.pdf