I *think* you can change the divert delay online, though the other options on that page do not - and possibly will not - work. CS are aware of the voicemail problem but that seems to be the extent of ...
Calls will be charged at standard geographic rates, so if you get free calls to 01- and 02- numbers at eve/weekends or whatever, then calls to a non-0845 W&T no would be free. Personally I can't ...