You beep someone when you call them up on their mobile phone--setting its display screen briefly flashing--then hang up half a second later, before they have had a chance to answer. Your friend--you hope--sees your name and number on their list of "Missed Calls" and calls you back at his or her expense.

It is a tactic born out of ingenuity and necessity, according to analysts who have tracked an explosion in miskin calls by cash-strapped cell phone users from Cape Town to Cairo.