all according, are you keeping your uk mobile or buying Turkish mobile...
UK from Turkey on uk phone I found expensive, still got my uk phone but only use it in when visiting the uk,it was getting expensive to phone friends and family (O2)maybe different on other networks.
I now have a Turkish mobile and cheaper for both parties uk to Turkey and vice versa.
If you are going to be living here then better to get a Turkish mobile until you have a landline,
but your question, if you are using UK mobile and friends phone you , no they will not need a code. dial as if you are in the UK.