Its not possible to unlock BB5 handsets using any known public method, they can only be unlocked by the network... Anyone who claims they can is either lying and will give you a dodgy random number generator or they will charge you more than the networks charge you and then just request the unlocking code for you from the network.
E.G Orange - Charge you £35, register a Pay as You Go Sim, top up with £20 credit and then ask Orange to use that credit to send them the unlock code. The best thing about this little trick/con is a lot of the phone shops usually get some sim cards which have already got some credit on there... for example if they buy some cheap phones from CPW they get £10 on each sim, they then transfer the balance from 2 sims to one, so they have £20 of credit and use that
An unlocked phone should work fine, once it is unlocked, unlocking is just removing the sim lock to accept other sim cards, the phones are originally designed to work on different networks, if the phone doesnt work properly its usually due to dodgy firmware, e.g Three