complicated process but turkish phones arent the cheapest to buy
if you have an old english mobile then as Don said you can take it over and have it registered as a turkish phone in the shops in
marmaris this must be registered to a british passport with someone that is over 18 and you can only register one phone every 2 years
once the phone is registered as turkish it cant be changed back
also it takes about 10 days to activate it so you wont be able to use it straight away
also there will be cheaper phones than 220tl go into marmaris they will have a much better selection

hope this helps
i have done the process myself of registering the phone so if you need to know anything else please dont hesitate to ask

xxx