It cost me 40zl to get mine unlocked, the phone is about 2 years old, though I've been told it can be done for less than that.
Related:What is the best mobile network to go on in the UK?
i am moving to UK and will need a mobile - i will occasionally be calling Poland so a mobile carrier with good international rates would be good.
Get yourself a laptop, put some credit on there, and use skype. It is so dam cheap and you can call free to other computers. Otherwise try orange they usually have good deals when phoning abroad. Calling abroad from the Uk is very over priced on all networks.