I saw this link on the homepage of "3" website.
It says:
When you call a friend on a different mobile network, or call their mobile from your landline, their network will charge your operator a fee for carrying the call.
This is called a Mobile Termination Rate or MTR and is currently charged at around
4.7p or more for every minute of the call.
The billions of minutes for which this fee is charged adds up to billions of pounds for UK consumers every year.
We think Mobile Termination Rates are excessive and distort competition. So we want the industry regulator, Ofcom, to lower the rate to reflect actual costs.
sign the petition: http://www.terminatetherate.org/?ver=www.three.co.uk
BT & Three are currently supporting this which is good