The speed of light, or more generally, the speed of electromagnetic waves, seems to be incredibly high. 300 000 km s[superscript -1] is far greater than the typical speed of a car, a plane or even a rocket, which is just several kilometres per second. It is thus natural that we treat the speed of light as infinite in everyday life. It appears, however, that even such a high but finite speed causes problems that have to be solved in one of the most popular electronic devices--cellular phones. Here we look more closely how the global system for mobile communications (GSM) phone works and how it deals with the speed of electromagnetic waves. (Contains 6 figures.)