For those of us in New York, Los Angeles, Chicago, and San Francisco, AT&T is giving us the opportunity to get text alerts about new products, special offers, and events from your favorite brands when your phone tells them you're nearby relevant stores.
This is called Geo-fencing (when you walk inside the imaginary fence around a geographical location, something happens). AT&T is rolling this out with the help of PlaceCast: http://placecast.net/index.html.
At first this will be an easy service to provide. There will be a small number of brands with active offers in whatever area you're in. Over time though, especially in large cities (like the places where this is being rolled out), the amount of offers could become overwhelming and so the real trick to getting this right would be in Offer Filtering. If this service takes the time to understand what offers we really need and want, we'll be hooked. If not, it'll quickly become an annoyance.
Good luck, AT&T. Try not to spam us with a million non-relevant texts!
Update 8/8/2012: This service is no longer available. Changing the World is hard.