Yellowstone National Park is relatively remote, especially when you leave the "villages" scattered about the park. As a result, you might not find a cell or Wi-Fi signal on your travels.
Cell phone service may be available at Grant, Canyon, Mammoth Hot Springs, and Old Faithful. As a courtesy to others, turn off your phone while enjoying Yellowstone’s natural
Wi-Fi is not available in rustic settings, National Historic Landmarks, or historic lodging. The NPS does not provide Wi-Fi for visitor use at visitor centers. Concessioners may provide Wi-Fi to visitors for a fee.