Spain's mobile market runs on three networks that operate their own infrastructure — Movistar (Telefónica), Vodafone Spain and MasOrange (the merged Orange and MásMóvil group, which also carries the Yoigo brand) — plus a fast-growing fourth network from Digi, which currently combines its own build-out with national roaming onto Movistar's towers where its own antennas have not yet reached. Movistar has the widest rural and inland footprint thanks to low-band spectrum that penetrates buildings and mountain terrain better than higher frequencies, which matters in inland Castile, the Pyrenees foothills and smaller island towns; Vodafone and MasOrange are close competitors in cities and coastal resort areas. All three main networks report 4G population coverage above 98% and 5G in the low-to-mid 90s percent, with the densest 5G in Madrid, Barcelona, Valencia, Seville and Bilbao.

The Balearic Islands (Mallorca, Menorca, Ibiza, Formentera) and the Canary Islands (Tenerife, Gran Canaria, Lanzarote and the smaller islands) run on the same three national networks and are treated as part of the domestic Spanish market rather than as a separate roaming zone, so coverage quality there generally matches the mainland in and around the main towns and resort areas; smaller, less-developed islands and remote coastal stretches can still see thinner signal. A trip that starts on the mainland and continues to an island — or the reverse — does not need a second local arrangement.

Buying a physical Spanish prepaid SIM requires showing a passport (for non-EU visitors) or an EU national ID card at the point of sale, under Spain's telecoms identification law; this applies at Movistar, Vodafone and MasOrange stores as well as at many supermarkets, tobacconists (estancos) and department-store phone counters. It is a quick process — often under fifteen minutes — but it does mean a stop before the SIM works. A global data-only eSIM does not carry a new Spanish phone number, so it is not subject to that in-store identification step, and it can be installed before the flight leaves.

The practical sequence: install the eSIM profile over Wi-Fi before departure, keep the home SIM active for calls, SMS and one-time passcodes, then switch the data eSIM on once the plane lands — whether that landing is in Madrid, Barcelona, Palma or one of the Canary Islands.

A Spanish prepaid SIM is genuinely easy to get — a passport is enough, no residency paperwork required — but it still means a store visit and, since 2007, mandatory registration of the buyer's identity under Spanish telecoms law. A data-only travel eSIM skips that step because it is not issuing a Spanish phone number. The trade-off is the usual one: no local number for calls or SMS, data only, with the home SIM left in place for anything that needs to keep ringing on the usual number.