Gibraltar runs on UK-based mobile networks (Gibtelecom, GibFibre and others). For your phone it counts as ‘rest of world’, not Spain or the EU.
Many Spanish and EU plans do not include free roaming in Gibraltar. Without checking, a few minutes on data can become an expensive bill.
Before crossing, contact your operator to enable a Gibraltar-friendly bundle, or simply disable mobile data at the border and rely on free Wi-Fi in cafés and hotels.
Local prepaid SIMs are available in Gibraltar but only worth it for longer stays. For a day trip, prepared offline maps and translated pages are usually enough.
