PayPal (eBay) will launch PayPal Mobile in a couple of weeks. A text message (SMS) or a voice call (IVR) can be used to transfer funds. It can be used for person-to-person payments or for buying stuff. The 'text to buy' feature would allow magazine readers to buy an item using a code in an ad. The item will be shipped to the address tied to the phone, which must be registered at PayPal.
Looks really easy and it must be a potentially fairly big market.