It may not automatically sit in either. It is French territory and part of the European Union, yet it stands on the South American continent, and regional bundles group it differently from one provider to the next. The only certain check is to open the plan's territory list and look for French Guiana by name. If the trip crosses into Brazil or Suriname as well, check those countries separately, because they are different networks in different countries.

It happens routinely, because the rivers marking the border are not wide and towers on the far bank reach across. If your plan covers only French Guiana, go into the network settings, switch to manual selection and lock onto a French Guiana network, and switch data roaming off on your original SIM as well. That way you are not billed by a network you never meant to use while standing on the bank waiting for the boat.

Plan from the start as though there will be nothing. A trip up the Maroni or the Oyapock takes hours or days, and forest villages are not wired into the coastal network. Before you leave, save offline maps, keep your guide's and lodge's numbers on the device, tell someone in town when you are due back, and carry a power bank, because in many villages the electricity runs for set hours rather than all day.

On launch day people come from all over the territory to the viewing points along the coast, so the network there is far busier than usual in the hour before lift-off. Check the latest launch time while you are still in town, save the viewing spot and the parking offline, agree a meeting point with your group in advance in case messages will not go through, and allow for the schedule slipping at short notice because of weather, which happens regularly.

Most plans here start when the phone first connects to a network at the destination, so you can install in advance at home and switch it on after landing. Each plan page states its own rule.

No. The eSIM is a second line, so you keep your home number for SMS OTP. Turn off roaming data on the home line and set the eSIM as the data line.