Mamoudzou: As the capital on Grande-Terre, Mamoudzou has the most extensive 4G/LTE coverage. The signal is strong in the city center, commercial areas, and around the main market. Indoor reception in dense concrete buildings can be less reliable. At the ferry port for the crossing to Petite-Terre, connectivity is excellent.

Dzaoudzi: Situated on Petite-Terre, Dzaoudzi benefits from solid network coverage, especially around the Dzaoudzi-Pamandzi International Airport (DZA) and the town center. The signal is generally stable on the ferry-known as the barge-that connects to Mamoudzou, though minor dips can occur mid-channel.

Koungou: Just north of the capital, this large and populous commune has dependable 4G signal along the main coastal road and in its central areas. As you move into more residential neighborhoods or further inland away from the coast, indoor coverage may vary and signal strength can be slightly weaker.

Sada: As a key town on the west coast, Sada's town center is well-served by 4G networks, providing a good connection for general use. However, coverage can become less consistent as you travel to surrounding beaches or more rural parts of the commune, where the signal might occasionally drop to slower speeds.

National Roads (RN1 & RN2): Coverage is generally reliable along the main RN1 ring road, especially in and around the capital, Mamoudzou, and other major towns. However, signal can become inconsistent or drop entirely on stretches passing through the island's hilly and forested interior, particularly between western and eastern coastal villages.

Dzaoudzi-Mamoudzou Ferry: The essential ferry link, known as 'Le Barge', connecting Petite-Terre (airport) and Grande-Terre (capital), maintains a strong and continuous cellular signal for the entire duration of the short crossing.

Central Mountainous Region: Traversing the interior of Grande-Terre, especially in the forests around Mont Bénara and through the Col de Combani pass, often results in significant signal degradation. Expect intermittent service or complete dead zones on smaller roads that cut across the island's rugged center.

Remote Coastlines and Islets: While the eastern coast near Mamoudzou is well-served, connectivity can be weaker along the more isolated western coastline and in smaller fishing villages. Service on the surrounding islets away from Grande-Terre and Petite-Terre is often limited or unavailable.

The Lagoon: Mobile signal is strong when boating close to the main islands. However, as you travel further out into the vast lagoon towards the outer coral reef or to more remote islets for diving or exploring, the signal will weaken and eventually disappear.