Greece's mobile market runs on three national networks with their own infrastructure: Cosmote (OTE), Vodafone Greece and Nova (formerly Wind Hellas). Cosmote has the broadest reach across mainland Greece, the Peloponnese and most inhabited islands, including smaller Cycladic and Dodecanese destinations where the other two can thin out; Vodafone Greece and Nova compete closely in Athens, Thessaloniki and the main resort islands. All three report population-level 4G coverage above 98% and have been extending 5G through Athens, Thessaloniki, Heraklion and the busiest island ports, though remote coves, ferry mid-channel and mountain villages in the Pindus range still depend mainly on 4G or occasional dead zones regardless of provider.

Island-hopping is where connectivity planning diverges from a single-city trip. High-speed ferries and some Blue Star or Seajets routes advertise onboard Wi-Fi, but it is a shared connection with limited bandwidth, often blocked or unusable once the vessel leaves the harbour and sometimes switched off entirely on shorter crossings. A phone with its own mobile data stays connected through departure, the open sea and arrival at the next port — useful for live ferry tracking, hotel check-ins and ride-hailing at busy island harbours where everyone else is hunting for the same ferry-terminal signal. The same eSIM and balance cover Piraeus, Rafina and the island ports without treating any leg as a separate zone.

Buying a local Greek prepaid SIM or eSIM from a domestic carrier requires passport-based identity registration under Greek telecoms law — a quick process at a Cosmote, Vodafone or Nova store, but still a stop before the line works. A global data-only eSIM does not issue a Greek phone number, so it is not subject to that in-store registration step and can be installed before the outbound flight. The trade-off is the usual one for travel eSIMs: data only, with the home SIM left active for calls, SMS and banking passcodes on the usual number.

The practical sequence for an island-hopping itinerary: install the eSIM profile over Wi-Fi before departure, keep the home SIM as the primary line for anything that must keep ringing, then switch on or select the data eSIM once landed — whether that landing is Athens, Thessaloniki or a direct island airport — and leave it active through ferry crossings rather than relying on onboard Wi-Fi for maps or messaging at sea.

A Greek prepaid SIM from Cosmote, Vodafone or Nova requires passport-based identity registration at the point of sale under Greek telecoms law — straightforward at a staffed store, but it still means a stop before the SIM works. A data-only travel eSIM skips that step because it does not issue a Greek phone number. The home SIM continues to handle calls and passcodes while the eSIM carries data across mainland and island legs on the same balance.