SIM cards and internet in the Triple Frontier: how to avoid roaming by accident

Direct answer: The most expensive mistake of the trip is accidental roaming: in the border strip your phone connects on its own to a Paraguayan or Argentine tower, and the international data charge lands even though you never crossed. The defence is to turn off data roaming or lock network selection to your own carrier. As for the end of Mercosur roaming: the agreement was promulgated in December 2025, but Brazil's telecoms regulator Anatel says it is not operational yet, with no set date. Until then, anyone needing internet across the border uses an eSIM, a local SIM, or a roaming package bought in advance.

The costly mistake: charged without crossing

Foz do Iguaçu sits a few hundred metres from Paraguay and Argentina, separated by rivers. Mobile towers do not respect rivers: the signal carries across. Near the Friendship Bridge, the Three Borders Landmark and at points inside the National Park, your phone may pick a foreign tower on its own simply because it is the stronger signal at that moment.

What counts for your carrier is the network the handset registered on, not the ground you are standing on. Travellers regularly report being billed for international data without having left Brazil.

How to protect yourself, before you arrive:

• Turn off data roaming in your phone settings. It is the simplest lock and it solves most cases.
• Or lock network selection: switch off automatic selection and pick your own carrier by hand.
• Watch the network name at the top of the screen. An unfamiliar name while you are in Foz is exactly this happening.

Is Mercosur roaming free yet? Not yet

This is the question of the moment, and the short answer is not in practice.

The agreement to eliminate international roaming charges between Mercosur countries was signed in Santa Fe on 17 July 2019. Turning it into Brazilian law took years: it was approved by Legislative Decree nº 192 of 2 September 2025, the instrument of ratification was deposited on 22 October 2025, and the agreement entered into force for Brazil on 21 November 2025. Promulgation came with Decree nº 12,782 of 18 December 2025.

What the agreement promises is straightforward: anyone using a phone in another member country should pay the same as they pay at home, according to the plan they already hold.

The gap is between being in force and actually working. According to Anatel, the measure, although in force, is not yet operational, and there is no set date for the regulators of the four countries to settle the model that will replace roaming.

So if someone tells you that you can already use your phone in Paraguay at home rates, check with your carrier first. Some carriers do sell their own South America packages today, but that is their commercial offer, not the agreement.

Your options today

Buying a local SIM, country by country

In none of the three countries do you need to be a resident. A passport is enough, and the line is registered in your name.

• Paraguay: the carriers are Tigo, Personal and Claro. For prepaid, a passport normally suffices, with no local ID required. Easy to find across the Ciudad del Este shops.
• Argentina: the carriers are Claro, Movistar and Personal. The line must be registered with a passport or another valid travel document. Claro and Movistar both run tourist-specific pages.
• Brazil: prepaid sales require the buyer to be registered, under Law nº 10.703/2003. For foreign visitors, Anatel's guidance to carriers is to accept a passport in place of the Brazilian CPF number.

Choosing without getting it wrong

• Crossing for a few hours to shop or see the Argentine park: turn off data roaming, download the map beforehand and use wi-fi. You do not need to buy anything.
• Spending days moving across all three sides: a regional eSIM is the simplest route, because it switches networks on its own at the border.
• Staying weeks, or living in the region: a local SIM from the country where you spend most time pays off.

Before crossing, check the live bridge queue.

Sources: Decree nº 12,782 of 18/12/2025 (promulgating the Mercosur agreement) · Anatel (status of the regulation) · Law nº 10.703/2003 · official carrier pages in the three countries · verified 11/09/2026.