North Cyprus has two mobile service operators, namely KKTCell (Kuzey Kıbrıs Turkcell) which everyone calls Turkcell which is actually the parent company based in Turkey. Then there’s Telsim which is now owned in part by Vodafone. Mobile numbers generaly start with 0553, 0542, 0548 or 0539.
Both companies can offer competitive service rates, with GPRS, 3G as well as standard tariffs available. It’s who you prefer really, although KKTCell does seem to have a hold on the market at present. They both also offer your itemised billing via email, and have English speaking staff at their offices which are in all major towns and villages and even in some supermarkets. Staff can assist you with any problems that you may have with a phone or help you configure your phone for any number of applications and services.
Both companies operate on GSM, 850, 900, 1800, and 1900 which most modern day mobile phones seem to be configured for (unless you still own a brick that is!), so you should have no problems in North Cyprus. If you want to use your UK number whilst you are holidaying here, then KKTCell and Telsim both have agreements in place with all major worldwide networks, so you should not have a problem connecting to their networks on your arrival.
Roaming fees however can be very high at times, so if you are planning on staying in North Cyprus for long periods, then you are much better off buying a pay as you go sim 
card from either operator, or purchasing a new mobile with the sim card, or getting your current mobile ‘unlocked’ to enable an additional operator other than your current UK or other network.
KKTCells and Telsims’ websites are KKTCell (which does have an English version) and KKTC Telsim (only in Turkish currently).
