Such a model was recently used by US West to calculate costs by US Census block groups, "Targeting High Cost Funding to High Cost Areas Using US Census Block Groups", draft US West, October 28, 1994.
Such Mechanism vary in detail but all follow the general mechanism described in: B. L. Egan, and S. S. Wildman, "Funding the Public Telecommunications Infrastructure", Telematics and Informatics, Vol. 11, No. 3 1994 (with Steven S. Wildman), also see the references therein.