The Federal Institute of Telecommunications (IFT) said America Movil SAB de CV, which is trying to downsize to avoid tougher regulation, will be able to charge companies that use its network between 0.005162 pesos and 0.006246 pesos.
Companies such as Telefonica and Nextel, which are exempted from the measures imposed on America Movil because of their smaller market shares, will be able to charge 0.2505 pesos.
The government completed a major reform in 2014 designed to loosen Slim's hold on the market he has dominated for years. Next year could also see the arrival of US company AT&T Inc to compete with the billionaire.
Earlier this month, the IFT approved AT&T's $1.7 billion purchase of Iusacell, Mexico's third-biggest mobile operator, which lags far behind America Movil.
Slim's company has around 70 percent of the mobile market in Mexico.