I've used ESTA quite a bit during the last few years for commuting, both the Lone Pine to Bishop and Bishop to Mammoth Lakes runs.
The bus from Bishop/Reno bus runs once a day four times a week, M, Tu, Th & Fr - northbound in the morning, southbound in the afternoon. They will stop wherever you ask them to and make scheduled stops in many of the towns along the way. Call ahead for pickup at alternative stops like Toms Place or Pine Creek or they will pass you by. It's a very popular mode of transportation in the winter for skiers and snowboarders heading to Mammoth Lakes.
The buses are fairly new, fairly clean and attract an unusual mix of individuals. They suggest making reservations for the Reno run and pickup/drop off at either the airport or the Greyhound Station. It's kinda pricy and is limited in daily offerings but all in all a good service for the area. I think if they had more trips scheduled they would have more users as it's still cheaper than driving.