Paul Golding would like the assistance of his mobile phone while shopping. I'll refrain from quoting his entire article, but I wanted to explore the concept a bit and see what's currently possible.
Fundamentally, I think there's a problem trying to convince shops to post their latest offers and essential product information via web services. Many mom-and-pop type stores just don't work that way. Stuff goes on clearance with little fanfare or forethought. The larger chains already publish their sale items on full-color flyers. A couple pages of newsprint is easier to read than most mobile phone displays. Is there really a need to wirelessly pull down the latest offers when you walk into a B&Q shop? Just pick up a flyer when you walk in the door.
I like the idea of being able to order something that's out of stock, but again, you don't really need a phone to do that. Any reasonably advanced store should be able to place an order with a swipe of your credit card and a hand entered SKU at the cash register. I can't say that I know any store that does this, but they should. It wouldn't require a cell phone so the service would appeal to a wider group of customers and it would probably be easier than fumbling with a phone.
Pushing advertising to your phone based on its GPS location is another good idea that comes with some warts. Currently phones don't broadcast their location to anybody, even the phone company. You have to actively request the phone to send a GPS fix by doing something with it like running an application, opening the browser or making a phone call. Periodically transmitting autonomously would certainly kill your battery in short order. Phones don't even constantly track location because that would run the battery flat almost as fast. Even if phones did constantly track GPS position, consider where you carry your phone. It will never get a fix sitting in your pocket or purse.
Aside from the technical issues, I have to wonder if consumers would really sign up to receive local spam. I suppose some might.
A simpler model might be Bluetooth push advertising. Bluetooth is designed to be short range and low power. Theoretically a local store could broadcast advertisements to Bluetooth phones and PDAs within 100 meters. That idea has been kicked around ever since Bluetooth was first envisioned but I'm not aware of anybody doing it on a large scale. Instead, Bluejacking seems to get all the press and I suspect people will be turning off their Bluetooth radios.