Some airports, often smaller ones, do not have a ground frequency. Not much changes from the controller’s point of view, but pilots must take extra caution when taxiing to and from their runway.
The pilot should pushback and taxi to a runway at their discretion, announcing all intentions over Unicom. No communication with Tower is needed until the pilot is ready for takeoff. If Tower on guards the aircraft, it is most likely because progressive taxi instructions are necessary. The pilot should follow all instruction from Tower, regardless of where they are and what the are doing.
References: Infinite Flight Pilot Communications Manual