In order to suggest an appropriate regulatory regime in the context of firm asymmetry, this study has developed a mathematical model that allows to elucidate comparisons of three different regulatory scenarios. In the unregulated market, the low-cost firm is more likely to become dominant in the market. Symmetric regulation has an immediate effect on off-net prices, which fall to the level of its marginal costs. Finally, asymmetric regulation is a highly effective way of promoting market entry. Asymmetric regulation can generate higher social welfare.