A couple quick points: I also lean towards Jerom and Deanya's interpretation. The question isn't just about location, it's an invitation for the other person to tell a bit about their availability. In addition to "where you at?" I've heard a lot of "what are you up to?" and "who are you with?" occurring early in conversations (I study teenagers). This information helps the caller know how to proceed with the conversation (e.g. what are they interrupting, how available is the other at this time). Simply picking up the phone doesn't indicate unfettered availability. As for the Boost adds, they refer to "chirping" (or "bleeping") which isn't quite the same as making a phone call. From my observations, the protocols for building up and tearing down conversations are much less burdensome with chirping. "Where you at" with Boost seems similar to pinging someone on IM, feeling out if the other is available to talk or even maybe even to meet up in person. Although I haven't looked at it, I'd imagine it's often considered reasonable to ignore a chirp (like an IM ping) or to respond with a quick indication that they can't talk right now. - Christo