I saw this deal the other day at Phones4u.If you've got the contract I think you have it's a free 8520 on the O2 100 tarriff on a 24 month contract for £15 a month.The problem is it doesn't include BIS which is a bit pointless really.
O2 have 2 different contract Blackberry bolt ons,an unlimited one for £10 a month and a pay per use one where you pay a whopping £2.56 per MB and you are going to need one of them to use internet related services.You will find the details
here.