Peru

Along most of the four-day trek there's no cellular coverage — the trail runs through a national park far from any towers. Save all booking details and guide contacts offline in advance.

Signal at the citadel itself is noticeably weaker than in Aguas Calientes below, and drops out entirely in places. Save your ticket and bus schedule on your phone before heading up.

It helps — you can quickly find a pharmacy or clinic near the hotel and message about how you're feeling if acclimatizing is harder than expected. Coverage in central Cusco itself is reliable.

Yes, the profile can be installed in advance via QR code or quick install, with data roaming switched on only after landing in Lima or Cusco, so the plan isn't used up before arrival.