No, free roaming with EU, UK, or US mobile plans typically does not apply in Saint Martin (SXM), which is outside these zones.
Despite the French side of the island being an overseas collectivity of France, most EU mobile carriers treat Saint Martin as an international roaming destination, meaning standard "Roam Like At Home" benefits usually do not apply. This is also true for the Dutch side, Sint Maarten, which is outside the EU roaming zone. Similarly, UK and US mobile plans rarely include Saint Martin in their free roaming zones. Attempting to use your home plan without an international roaming package can lead to extremely high charges for data, calls, and texts.
To avoid unexpected bills, consider purchasing a local SIM card upon arrival or, for a more convenient option, an eSIM. An eSIM allows you to connect to major local networks like Digicel or Flow at much more affordable rates, ensuring you stay connected throughout your trip to both the French and Dutch sides of the island.