Look through and join yahoo group waypointsdotph. You can download a routable map of the Philippines for most handheld garmin units (maybe not for the nuvi as the maps are preloaded by Garmin).

Inexpensive Bluetooth GPS receivers can be paired with PDAs and PCs(laptop,notebook,desktop) and a lot of mapping and navigational softwares are available (some free). Mapking Manila gives you a routable Metro Manila Map.