Regarding craigp and dougs first post, global communications have phoned me several times now, firstly i think i got the same guy Doug got and found little help off him.
Yesterday a lady phoned me and was very helpfull, i also got out of her that if you use BT call diversion, the *21* type, instead of diverting to your mobile phone, divert it to your 0800 free number which in turn you have diverted to your mobile, you then are not paying for the usual diversion to your mobile.
Might be worth another look if this is the case, deal was one off of £150, for 1000 minutes per month and they will stand the first month if you go over your limit,
a very helpfull lady she was.
Andrew