google voice number and google hangouts and being overseas
Merhaba! I live in Istanbul as well, and use my pre-existing Hangouts/Voice number just fine, on a phone I bought here in Turkey. I just logged into my Google account on my new phone, and everything worked. You should be just fine! 

Your Voice account is tied only to your Google account, not any US number. I've completely deleted any US number from my account, and there was no issue whatsoever.

You won't be able to automatically forward Google Voice calls to your Turkish number, but you will receive &amp; make calls &amp; texts via the app (over your 3g/wifi connection). 

saygılar
~peter