They have been doing this for years in Japan. Indeed, there are several ways to use ones phone for buying stuff.

One can go from one end of the country to the other with nothing other than one's phone. (Unless it's an iphone, then you need a REAL phone too.)

(Although the fancy-pants iCrap and Android stuff is not actually useful for taxis, train tickets or convenience stores. It might work for plane tickets, different system.)

They're an internet appliance, of course people will buy from them.