San Juan: As the capital, San Juan offers excellent 4G LTE and growing 5G coverage across its main districts, including Condado, Santurce, and Isla Verde. In the historic Old San Juan, the dense colonial-era buildings can occasionally weaken indoor signals. The Tren Urbano rail system provides reliable connectivity at its stations, but the signal can be intermittent in the underground tunnel between the Universidad and Río Piedras stations.

Ponce: Puerto Rico's second-largest city boasts strong and reliable network performance throughout its urban core and historic downtown area. You'll find a stable connection for navigating and sharing photos. Coverage can become less consistent if you travel into the mountainous regions of the Cordillera Central just outside the city.

Mayagüez: Located on the west coast, Mayagüez provides dependable cellular service, particularly around its downtown plaza and the University of Puerto Rico campus. While the city itself is well-covered, signal strength may diminish in the more rural and hilly areas further inland.

Bayamón: A major part of the San Juan metropolitan area, Bayamón has robust 4G and 5G coverage suitable for all urban activities. The sections of the Tren Urbano that run through the city are mostly elevated, ensuring a more consistent and stable mobile connection for passengers compared to the underground portions elsewhere.

Fajardo: This eastern coastal hub, critical for tourists heading to nearby islands, has good overall coverage within the town and at the ferry terminal. Be aware that your signal may fluctuate during the ferry crossings to Vieques and Culebra and can be limited within the dense canopy of the nearby El Yunque National Forest.

Major Expressways (Autopistas): Connectivity is generally strong along the main toll roads like PR-52 (connecting San Juan to Ponce) and PR-22 (connecting San Juan to Arecibo). You may experience brief signal degradation in more rural segments between major urban centers. Non-toll highways like PR-2 and PR-3 also have reliable coverage but can have more frequent gaps in less populated coastal areas.

Intercity Rail: Puerto Rico does not have an intercity passenger rail system. The Tren Urbano is a metro system operating exclusively within the San Juan metropolitan area, where it maintains generally good cell signal, with brief drops in underground sections.

Cordillera Central Mountains: Driving through the island's central mountain range will result in significant and frequent signal loss. Routes like PR-10 (from Ponce to Arecibo), PR-155, and the scenic Ruta Panorámica have long stretches with intermittent or no service, especially within deep valleys and forested reserves.

Vieques and Culebra Islands: While the main towns have coverage, service is very weak or non-existent across remote parts of these islands, including many popular beaches and nature reserves. The ferry journey from the main island also has unreliable connectivity.

Highway Tunnels: Expect to lose your signal completely inside major highway tunnels, such as the Túnel Minillas on PR-22 in San Juan or the Vicente Morales Lebrón Tunnel on PR-10. Service typically resumes immediately upon exiting.