Roaming charges for customers of cellular-wireless entrant providers

We consider a simple two-player game involving a large incumbent and small entrant into a cellular wireless access provider marketplace. The entrant´s customers must pay roaming charges. We assume that the roaming charges are regulated to prevent an incumbent from creating barriers to entry in the marketplace. The game is studied at its Nash equilibrium. A roaming charge is identified that is arguably fair in the sense that revenues for the access providers are proportionate to their infrastructure costs.