Turkey limits how long a foreign phone can use local Turkish SIMs: after roughly 120 days the IMEI must be registered (with a significant fee) or the phone loses local-network service. Students, remote workers, and long-stay visitors hit this wall every year.
The roaming alternative
The rule targets foreign phones on local SIMs. A roaming eSIM isn't a local SIM — it keeps delivering data the same way your home carrier would while roaming, without registering your IMEI. For calls, WhatsApp and FaceTime work normally over data.
Practical notes
Turkcell's 4.5G network is fast in every city tourists and expats actually live in. Keep your home SIM active for SMS if you need bank codes. Rules can change — buy prepaid, never on subscription, and prefer stores that say so plainly.