I think that this article may be a good start.
Couldn't find a document backing it up but the post is from 9/18/07 and clearly reads:
Sprint and Microsoft Debut Location-Aware Local Search
...The GPS location-aware that's going to automatically figure out what city you mean when you're searching for "Sushi Restaurants" isn't actual GPS—it's cellphone tower-based triangulation—but that's more than enough to figure out what city you're in. They're also introducing Tellme by Mobile, which is a voice interface to local searches, but since it's not a native Windows Mobile app, it may be slightly less stable and/or pleasing to use than the Live Search.
And the publication on the Microsoft site:
With the enhanced mobile search service launching today, Sprint customers can now:
Use Sprint’s built-in GPS capabilities to automatically find local businesses and listings nearby quickly and easily without needing to manually enter location information. The new GPS-enabled search allows customers to give permission to let their phone automatically identify their location to return nearby business search results, such as the closest gas station, pizza place or movie theater – all by simply typing in or, on select phones, speaking the name or category of business for which they are searching.