There's websites that show coverage maps for the main providers so you can check exactly what the coverage is like for each in your area. They can vary quite a bit.
Did the gym say you can get a DTV with a course that is just coming in once or twice a week? When I looked at MT visa-ready courses they were really full on, not just a drop in occasionally type of deal.
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.