What you need is a usb cable and a dct-4 calculator ( code calculator 5.4 is a good one ), a google comes up with :-
http://www.peters1.dk/webtools/nokia/nokia.php?sprog=en
This supports the 2300 however it should do the 2310.
And those dodgy mobile shops, all they do is use this or some hardware ( for bb5 phones, similar to http://www.fonefunshop.co.uk/Unlocking/bb5box.htm ) that enables them to delete all the software and firmware and reinstall it without the operator crap.
All at your own risk.