How to unlock my iphone again (i went abroad)?

I live in the UK and i was on 3 network, my iPhone 5 is was unlocked as i got it from the Apple store. When i went to Turkey i used a different sim card to avoid the cost of data roaming and my iPhone got locked to it. Now every time i enter my 3 sim card it gives me "no service". I went to the 3 store the other day and explained my problem, one of the staff members said something about connecting it to iTunes and backing my iPhone up and then i should get it unlocked to use the 3 sim card again. I don't quiet remember what the procedure was can someone help me? As i hate being out of reach.

I don't think your phone is unlocked fully, it was software unlocked and when you use the new SIM, your phone got locked. If you need help with getting the phone factory unlocked, mail me.