Can you place a foreign SIM card in a mobile purchased in Turkey?

They are not switching off foreign phones with foreign numbers.  They are switching off foreign phones with Turkish SIM card.

I have 2 mobiles and 2 sim cards. One is my mobile from my country and  it is working without problems last 2 years with my SIM card. I only switch off mobile data not to use internet from home. You can do whatever you want with your mobile phone, but you must know it is very expensive to call with that number.

Second number and phone are Turkish. So, I am using internet with that phone and with hot spot I am connected with my other phone.

In Turkey it is a problem if you are using Turkish SIM card in the phone which you bought in some other country. In that case they will cut your line after 3 months, or you need to pay taxes to the country which are very high, 6091.30 TL which is 300 Euro. So, you need to buy phone in Turkey but the phones are also very expensive.  It will be best for you to borrow phone from friend or from some company. If you are buying phone second hand, do it with Turkish friend because if the phone is stolen you will be in a big trouble. When you will by SIM card, they will register your number and your phone.