3's WePay rewards users for taking calls

Ok, so here's the gimmick: you sign up for pay-as-you-go-service with 3 (they're a British carrier, remember?), and they pay you out airtime credits for getting calls or texts from your mates. They call it WePay, and apparently a five minute call will net you credits enough for two texts or an MMS (or a bit of mobile TV, if that suits your fancy); 100 minutes of calling or 50 texts will pay you out £6 in credits. Seems like as long as they're keeping their margins high enough over the "discount" provided with credit paybacks, doesn't sound like 3 should have much of a problem with this one -- that is, unless everyone in England switches to WePay and no one calls each other anymore, expecting others instead to call them to pump up their credits.