Irrespective of what you pay for 01, 02 and 03 calls, by moving away from BT you'll likely lose inclusive 0845 calls (though even BT customers will have to live with that reality in about 18 months time) or see their price rise considerably, as well as see calls to 0843, 0844, 0871, 0872 and 0873 numbers perhaps almost double in price.