Factors determining the diffusion of digital mobile telephony across developed and developing countries are studied with the aid of a Gompertz model. After controlling for other factors, the speed of diffusion per se is not significantly different between the two groups of countries. Standards competition hinders and market competition promotes diffusion in both groups. Various factors are, however, more important in a developing country context: having a large potential user base, accumulating network effects, being open, commanding a high (non-telecom) technological level, and introducing innovation(s) complementing mobile telephony. Late entrants experience faster diffusion promoting cross-country convergence.