The short answer: buy and install your Turkey eSIM before you fly. Since July 2025 the Turkish regulator, BTK, has blocked the websites and apps of every major travel-eSIM provider from inside the country, so an eSIM you have not pre-installed cannot be purchased or topped up after you land without a VPN — and most VPNs are blocked too. The eSIM itself works perfectly once installed; only the storefronts are blocked. For most US and UK travelers on a city-and-coast trip, our pick is Airalo's Turkey eSIM on the Türk Telekom network — install it at home and it activates the moment you land in Istanbul. If your trip runs deep into Cappadocia's valleys or eastern Turkey, choose a Turkcell-hosted eSIM instead (Saily or Holafly), because Turkcell is the only network with reliable rural signal. Which Turkey eSIM fits your trip? For a city break in Istanbul, Ankara or Izmir, Airalo's 7-day unlimited ($27) on Türk Telekom is the clean pick. For Cappadocia, the coast or eastern Turkey, choose Saily or Holafly on Turkcell. For heavy data or tethering, Nomad's fixed 20 GB ($21) or 50 GB ($31) plans run at full speed with no daily throttle. For budget or light use, Saily 3 GB or Ubigi 3 GB cost about $7. For multi-country trips, Airalo Eurolink includes Türkiye across about 39 countries. For simplicity, Holafly unlimited works, but its hotspot is capped — not for family tethering. Why you must buy before you fly: the BTK app block. On July 10, 2025, Turkey's Information and Communication Technologies Authority (BTK) issued an administrative decision blocking access to the websites and apps of international eSIM providers from inside Turkey. The original list named Airalo, Holafly, Saily, Nomad, aloSIM, BNESIM, Instabridge and Mobimatter; follow-up decisions expanded it to 35-plus providers. An on-the-ground test in Istanbul in May 2026 confirmed 23 providers still blocked. The nuance that matters: any eSIM you bought and installed before arrival runs normally on the host Turkish network; what you cannot do is buy a new plan or top up while physically in Turkey. Ubigi states on its own site that travelers must install and activate before the flight because its app and website are inaccessible from within Turkey. You cannot reliably fix this with a VPN once you land — Turkey uses deep packet inspection to drop OpenVPN, WireGuard and IPSec, and roughly 27 commercial VPN services are blocked. The safe move is to buy more data than you think you'll need. The 120-day IMEI trap, and how a travel eSIM sidesteps it. When a foreign phone first connects to a Turkish network using a local Turkish SIM, its IMEI is logged and a 120-day countdown begins. On day 121, if the device is not registered and taxed through the e-Devlet portal, the IMEI is blacklisted across all three carriers and the phone permanently loses cellular service inside Turkey. The 2026 registration fee is ₺54,258 (roughly $1,200–$1,260). A 2026 enforcement update closed the dual-SIM workaround: as of May 1, 2026, swapping SIM slots no longer gains extra windows, and registration is limited to one device per passport every three years. The key point: a travel eSIM roams on a foreign profile, so it never registers your phone on a Turkish network and the 120-day counter is never triggered. The trap is the local SIM — if you put a Turkish tourist SIM in your phone, even alongside a travel eSIM, you start the clock on that hardware. 5G is brand new — plan for 4G. Commercial 5G launched on April 1, 2026, after the October 2025 spectrum auction, with meaningful coverage concentrated in the largest cities. Provider 5G badges are mostly aspirational for now; in practice you'll spend your trip on Turkey's mature 4.5G/LTE network. Treat Turkey as a 4G country when you plan. Networks and coverage: the host network decides your trip. Three operators run Turkey's networks. Turkcell (about 41% market share, ~75 Mbps median) has by far the best rural, mountain, coast and eastern coverage — the only reliable signal in deep Cappadocia and the east. Vodafone Türkiye (about 31%) is strong along the Aegean and Mediterranean coast. Türk Telekom (about 28%, 99.7% population 4G) is excellent in cities and is the wholesale host for Airalo, Nomad and Ubigi. Because most popular eSIMs ride Türk Telekom, they are great for Istanbul, Ankara and Izmir but weaker in the rural east; for Cappadocia's valleys or eastern Anatolia, pick a Turkcell-hosted eSIM. In Cappadocia you'll get a solid 25–45 Mbps in Göreme town, but signal thins in the deep valleys, and the Derinkuyu and Kaymaklı underground cities have no signal at all. The local tourist SIM is usually the wrong call. At Istanbul Airport, Türk Telekom's 20 GB data-only SIM runs about ₺1,935 (~$42) and Turkcell starts near ₺2,550 (~$56) — three to five times the price of a pre-bought eSIM, and airport SIMs cost 50–70% more than the same packs in city stores. Worse, buying any local SIM requires passport registration and ties your IMEI to a Turkish line, starting the 120-day clock a travel eSIM avoids entirely. Always pay in Turkish lira. VPNs and censorship: an eSIM is not a censorship bypass. Turkey throttled Instagram, X, WhatsApp, YouTube and TikTok for roughly 42 hours during the March 2025 protests and again in September 2025; PayPal has been blocked since 2016. A home-routed roaming eSIM may incidentally clear some site-level blocks, but during event-time bandwidth throttling even roaming connections slow to a crawl. For anything critical, set up an obfuscated VPN before you arrive. The bottom line for Turkey in 2026: buy and install your eSIM before you fly, match the host network to your route, and over-buy your data.