Costa Rica has three mobile operators: Kölbi (part of the state telecom ICE), Movistar Costa Rica (Telefónica), and Claro Costa Rica. Kölbi has the widest national coverage, especially in rural and mountainous areas. Movistar and Claro have strong urban coverage in the Central Valley (San José, Heredia, Alajuela, Cartago) and main tourist towns.
San José has excellent 4G coverage across the Metropolitan Area. The Juan Santamaría Airport area, La Sabana, Escazú, and the historic city center are all well covered. Arenal volcano area and La Fortuna have solid 4G from Kölbi. Manuel Antonio and Quepos on the Pacific coast have 4G in the resort strip and park entrance.
The Osa Peninsula and Corcovado National Park present a connectivity challenge. Drake Bay has limited 3G coverage. The park interior and Puerto Jiménez have weak to no signal on jungle trails. The Monteverde Cloud Forest area has variable 3G to 4G depending on your exact location in the cloud forest. Caribbean coast towns like Puerto Viejo de Talamanca have 4G from Kölbi. Remote national parks in the south including Chirripó and the Talamanca highlands have minimal signal. Download offline maps before any jungle, highland, or remote peninsula trip.