Be realistic about the trek
This is the honest part. Kathmandu and Pokhara are well covered, and the lower stretches of the popular trekking routes often have a signal. Higher up, and on the more remote circuits, you should plan for stretches with no coverage from any network at all. Teahouses sell Wi-Fi by the hour at altitude for exactly this reason. A data plan is for the cities, the planning, and the parts of the trail that do have a signal, not a guarantee of connectivity at Base Camp.

