Ok, so here's the gimmick: you sign up for pay-as-you-go-service with 3 (a British carrier), and they pay you out airtime credits for getting calls or texts from your mates. Called WePay, apparently a five minute call will net you credits enough for two texts or an MMS (or a bit of mobile TV); 100 minutes of calling or 50 texts will pay you out £6 in credits.