Do I need to register my foreign phone (IMEI) in Türkiye?

A phone brought from abroad and used with a Turkish SIM will keep working only for a limited period before the network blocks the device unless its IMEI is registered. Registration is a paid government procedure (done via e-Devlet / a tax office, and it involves a fee). The exact grace period and fee are set by the authorities and change, students in chats often quote different numbers, so treat those as unverified and check the current rule on the official e-Devlet service.