Yes, in key areas. You will have strong 4G/LTE in Antigua, Guatemala City, and the main towns around Lake Atitlán (like Panajachel and San Pedro).
- Tikal: You will have a signal in the nearby town of Flores and at the park entrance/main plaza, but it can be spotty in the deep jungle between remote temples.
- Acatenango: You will have a signal at the base camp and on the hike up, which is famously strong enough for hikers to upload videos of the Fuego volcano erupting at night.