It’s no secret that local discovery is becoming one of the central trends in mobile advertising. This replaces the search based paradigm that ruled the desktop, in favor of pushing content that is geographically relevant. The portability of the device and small keypad make that push scenario more appropriate.

Following the growth and feature rollouts of companies like Foursquare, Poynt and Where, the latest chapter in mobile local discovery is Placecast’s deal with AT&T. Much like its recent deal with O2 in Europe, this will utilize Placecast’s geofencing technology to push deals to users that enter predefined zones.

Those zones surround different retailers or areas prevalence for products of a given brand. In this case, AT&T is pushing offers from its launch partners including JetBlue, Khol’s, HP and Kmart. Users who opt in for the text alerts are sent deals from these brands when geographically relevant.

The deals will be initially available to AT&T mobile subscribers in New York, Los Angeles, Chicago and San Francisco, with other cities to follow. The program will be marketed by a combination of AT&T cross promotions and signage in and around the places where these brands are sold.

As we’ve said in the past, geofencing combined with this type of opt-in creates a nice balance between push and pull. It has the push-based discovery aspects mentioned above but also the presence of a self-selected audience of individuals who have already raised their hands to indicate a preference for receiving offers.

We’ll see other carriers and brands adopt this as Placecast continues to gain exposure and proof points. In addition to O2 and its advertisers in the U.K., Placecast has already worked with a number of brands directly to manage their mobile local offers, such as The North Face.

In similar news, Loopt has announced it will launch a new system of push notification system for local deals. This will be available to users of its iPhone and Android apps who can opt in and manage alerts within the app. Geotargeting happens via GPS tracking that’s central to the app.

It will first get this going at South by Southwest later this month by giving away $50,000 worth of merchandise, including Microsoft Kinnects and Southwest Airlines round trip tickets.