Ok, I've used GPS on a T3 and a Treo 650 - also used Garmin iQue 3600, M4, 3000, StreetPilot 2620, 2720, and Nuvi 350.
Bottom line - dedicated is the only way to go. And right now I'd recommend the Nuvi platform. It's very small but a powerful enough speaker to here it. Most Palm's don't have...