We've got some pretty cheap phones here in the States that are pay-as-you go — sometimes referred to as burners — though you probably haven't used too many of those unless you don't have a cellular plan or you're a drug dealer.
Vodafone is targeting the former with the Vodafone 150. It's a phone for the developing world that will debut for "well below" $15 in eight African countries. While the phone doesn't feature the kind of functionality it takes to cut it Stateside — such as a camera or a connection to the Internet — the cellphone market in developing countries is a goldmine opportunity for phonemakers, and cells act as vital a role there as they do here, such as providing access to a bank account or sending medical reminders.
When we see a phone like this in the US, it's usually pegged as something for the elderly.