Two Countries in One Day: 11 Border Trips and Your Phone

Set to choose its network automatically, a phone joins whichever network has the best signal where it is. Near a border, that can be a network on the other side. Romania's telecoms regulator, ANCOM, describes exactly this: phones in border areas joining a neighbouring country's network while their owners are still at home, and the roaming charges that follow, because using roaming by accident does not exempt you from paying for it.

Inside the European Union that usually costs nothing. Roam-like-at-home, the EU rule that lets a phone with an EU contract pay home prices abroad within its operator's fair use limits, covers the EU countries plus Iceland, Liechtenstein, Norway, Moldova and Ukraine. Switzerland and Monaco are not on that list, which matters on three of the trips below. Some operators include them anyway, so read your own operator's roaming terms before you go. Our guide on how to avoid roaming charges lists the settings to change first.

A travel eSIM turns the question from what roaming costs into which countries are on the plan. If both sides of the border are on it, the phone can cross and recross and nothing changes. If only one side is, the other side needs a plan of its own, or a plan that lists both. For each trip below we say which of our plans does that, and what it costs next to the alternatives.

If your home SIM stays switched on next to a travel eSIM, Apple's guidance is that the travel eSIM carries the data but the home line can still run up roaming fees. An iPhone uses one line for mobile data at a time, and its Allow Mobile Data Switching setting (Allow Cellular Data Switching in US English) lets data move to the other line depending on coverage, so leave that setting off unless the other line costs nothing where you are.

Before any of the trips below, four habits save most of the trouble.

• Install the plan for the other side before you set off. Its days start when it first connects, not when you install it.
• Close to the border, check which network the phone has joined before you use data. If it has crossed early, turn off automatic network selection and pick the network yourself.
• Carry the passport or ID card the crossing needs, even on a tram. Several of these borders have checks running this winter.
• Save the map of the other side for offline use, so a slow switch between networks does not leave you lost at the station.

The link between Denmark and Sweden is three structures in a row: about 8 kilometres of bridge, a 4-kilometre artificial island called Peberholm and 4 kilometres of tunnel, 15.9 kilometres in all, carrying road and rail. It has joined the two countries since 1 July 2000.

Take a passport or ID card. Sweden has told the European Commission it is running checks at its internal borders, the land border with Denmark included, from 12 November 2026 to 11 May 2027.

Both countries are in the EU, so an EU contract roams at home prices on either side. On a travel eSIM, all of our Europe plans cover Denmark and Sweden, and at one, three or five gigabytes the cheapest of them costs the same as a plan for one country. If you already hold a Denmark plan for the week, a one-day Sweden plan costs less than any other plan we sell for Sweden.

Basel's trams cross two borders. Tram 8 has run over the border to Weil am Rhein in Germany since 14 December 2014, and tram 3 runs to the railway station in Saint-Louis, France. Both are on Basel's ordinary city timetable.

Checks can still happen on either line. Germany has notified checks at its land border with Switzerland until 15 March 2027, and France at its borders with Switzerland until 30 April 2027, so carry what you would carry for any other border.

Switzerland is not in the EU roaming zone, so an EU phone can run up roaming charges in Basel itself unless its operator includes Switzerland. This close to two borders the phone can also pick up German or French networks, and a travel plan only works on the networks of the countries it lists. Our cheapest Europe plan that includes France covers Switzerland, Germany and France and, at one, three or five gigabytes, costs the same as a Switzerland plan. Check the list before you buy, because another of our Europe plans at the same price leaves France out. Our Switzerland guide covers the rest of the country's roaming quirks.

Since 1 July 2023 a chain of cable cars called the Matterhorn Alpine Crossing has linked Zermatt in Switzerland with Breuil-Cervinia in Italy, all year round. Its operators put the journey at 1.5 to 2 hours each way and suggest the return trip as a day out, about 3.5 hours of travel in total. At Testa Grigia, at 3,480 metres the highest border crossing in Europe by their account, you can stand with one foot in each country.

Two things to know this winter. The crossing shuts for maintenance from 7 January to 26 February 2027, while the cable car between Matterhorn Glacier Paradise and Testa Grigia is closed, and on days of doubtful weather the operators announce by 11 a.m. whether it runs. Testa Grigia is an official border, and the operators say you may need to show a valid identity document.

For the phone, this is the Basel problem at altitude: Italy is in the EU roaming zone and Switzerland is not, so an EU phone that roams free in Cervinia can be charged in Zermatt. Every one of our Europe plans covers both Switzerland and Italy, and the cheapest cost the same as one country up to five gigabytes. Our ski trip guide covers the resort countries the Europe plans leave out.

Monaco is the smallest place on this list and the most expensive one for your phone. It is not in the EU, so EU roaming rules do not reach it, and it is on none of our regional or global plans.

Monaco has plans of its own, and they cost far more than France's. The smallest is a one-day plan with one gigabyte, at about four times the price of a one-gigabyte week in France, and the three-gigabyte month costs about ten times the French one. There is no week-long Monaco plan and no unlimited one.

If a few hours without mobile data suits you, save the map, your tickets and whatever else you will want offline before leaving Nice, and use Wi-Fi in Monaco where you find it. If you need data there, add the one-day Monaco plan to your France plan and switch the data line when you arrive. Our guide to Monaco and Europe's other small states explains why the regional plans skip them.

On 15 July 2026 the treaty between the UK and the EU on Gibraltar began to apply, and the routine checks at the land border with Spain ended. Gibraltar's government marked the day as the end of controls at the frontier. Schengen checks now happen at Gibraltar's airport instead.

The walk in is still the strange part. Gibraltar's airport runway was built across Winston Churchill Avenue, the road from the frontier, in 1941, and before 2023 the road closed more than 15 times a day for flights. Since 31 March 2023 cars and motorbikes have used a tunnel instead, while people on foot, on bicycles and on scooters still cross the runway itself.

For the phone, Gibraltar is on some of our Europe plans and not on others, so check the list for this trip above all. Our cheapest Europe plan that includes France and Gibraltar covers both sides of this border and costs the same as a Spain plan up to five gigabytes, while another Europe plan at the same price leaves Gibraltar out. Gibraltar also has plans of its own, priced like Spain's at one, three and five gigabytes.

The RTS Link, a shuttle train between Woodlands North in Singapore and Bukit Chagar in Johor Bahru, is expected to start carrying passengers in February 2027. The ride should take about five minutes, and you clear immigration at the station you leave from. The date still depends on an independent safety certificate and on approval from both governments, so treat February as a target rather than a promise.

For the phone, this is the simplest crossing here. Our plan for Singapore, Malaysia and Thailand covers both ends of the line, and it costs the same as a Singapore plan for one gigabyte over a week, and the same as Singapore's three-gigabyte month for three gigabytes over fifteen days. Our Malaysia guide weighs it against one-day plans for longer stays.

Hong Kong to Macau is a crossing of a different kind. Shuttle buses run over the Hong Kong-Zhuhai-Macao Bridge between the two border ports day and night, and Macau's transport bureau lists both daytime and overnight fares. A Hong Kong plan does not cover Macau. From three gigabytes up, a Hong Kong plan plus a one-day Macau plan costs less than any of our plans that list both places, and our Hong Kong guide explains the networks on each side.

At Niagara Falls the Rainbow Bridge joins the American and Canadian sides, and you can walk across it: US Customs and Border Protection keeps a pedestrian lane there, open 24 hours a day. If you start on the Canadian side and come from a Visa Waiver country, you need an approved ESTA to enter the United States by land, just as you would by air.

South of San Diego, the San Ysidro crossing into Tijuana is, in the words of the US General Services Administration, the busiest land border crossing in the Western Hemisphere, with two buildings just for people crossing on foot.

For one day in Canada or Mexico on a US trip, the arithmetic depends on size. At one gigabyte, our plans for the United States and Canada, or for the United States, Canada and Mexico, cost the same as a US plan. Above that, a US plan plus a one-day Canada or Mexico plan costs less than either of them.

Colonia del Sacramento sits on the north shore of the Río de la Plata, facing Buenos Aires, and ferries cross the river between the two. The Portuguese founded it in 1680, and its historic quarter has been on UNESCO's World Heritage List since 1995.

Argentina and Uruguay are both on our six-country South America plan. At one gigabyte it costs about half of what an Argentina plan and the smallest Uruguay plan cost together, and at three gigabytes it still costs a little less. From five gigabytes up, the two country plans are cheaper. Uruguay has no one-day plan, so its smallest is a one-gigabyte week.

The King Fahd Causeway has linked Saudi Arabia and Bahrain since 1986, and it is 25 kilometres long.

Both of our six-country Gulf plans list Saudi Arabia and Bahrain, and the one that includes Iraq rather than Oman costs less. At one gigabyte it costs less than a Saudi plan and a Bahrain plan bought separately. Above that, a Saudi plan plus the smallest Bahrain plan costs less, and in Bahrain the smallest plan is the one-gigabyte week, which costs less than Bahrain's one-day plan. Our Middle East guide sets out what each Gulf plan covers.

Put the eleven trips side by side and the answer comes in five shapes.

• One plan at the price of one country: our cheapest Europe plan that includes France and Gibraltar covers Copenhagen and Malmö, Basel and its neighbours, Zermatt and Cervinia, and Spain and Gibraltar for what one country's plan costs, up to five gigabytes.
• The same for Singapore and Johor Bahru: the plan for Singapore, Malaysia and Thailand costs what a Singapore plan costs at one gigabyte, and at three gigabytes over fifteen days.
• A plan for where you sleep plus a small plan for the day: Niagara Falls and Tijuana above one gigabyte, Bahrain above one gigabyte, Macau from three gigabytes and Colonia from five.
• A plan that lists both, at small sizes: Niagara Falls, Tijuana and Bahrain at one gigabyte, and Colonia up to three.
• Monaco, where no plan of ours covers both sides and the one-day Monaco plan is the smallest purchase.

A one-day plan is not automatically the cheapest way to cover one day. In Denmark, Sweden, Switzerland, Germany, France, Italy, Spain, Malaysia, Hong Kong and Macau, our one-day plan costs less than the one-gigabyte week and carries two gigabytes. In Saudi Arabia, Bahrain, Mexico and Argentina it is the other way round, and in Canada the two cost the same.

One-day plans also cannot be topped up, and the plan card marks them No top-ups. If the day might run long, or you might come back later in the week, the one-gigabyte week, which does take top-ups, is the safer buy.

For a longer route through several countries, our guide to one eSIM for multiple countries compares regional and country plans.