That's new twangster, when I tried to pay by phone a month ago the only alternative was an 0845 number which is chargeable on most plans, not all.
They have replaced it with an 03 number which is free with mobile contracts but chargeable via land lines without a plan and pay as you go, which is where the local charges come in.
Good on RCI for changing it, lets hope they keep it that way.
I'm sorry twangster but I don't like getting ripped off no matter for how much, if you and the others here that disagree don't mind paying to pay your bill and other things that's fine, I'm not.