It doesn't even require that. All of those updates occur on different logical channels. (google Location Area Updates / Routing Area Updates and GSM or UMTS). All of that stuff takes place on the signaling side and doesn't even reach the systems that handle data billing. In GSM and earlier revisions of UMTS (3G), it is all handled over circuit switched, not packet switched.
AT&T is very capable of doing things the way you said though. All it has to do is assign certain communication to a different APN (as it does with visual voicemail on the iPhone, FOTA updates on any phone that does FOTA, etc...)