It's me again. First, I'd like to note that the link in the previous comment is incorrect, it should be osm.wiki/index.php/User:Vsevolod_Shorin. And second, gpsVP, apart from OSM maps support, also collects information about traffic. You can see it in this category - http://gpsvp.garminmapsearch.com/?cat=10. Good luck!

I also think that it would be useful to have a look at gpsVP (http://www.gpsvp.com) - GPS software for Windows Smartphones. Currently it supports:
- Windows Mobile Smartphone 5.0 or Windows Mobile 6 Standard (devices with keyboard and no touchscreen).
- Windows Mobile for PocketPC 5.0 or Windows Mobile 6 Professional (devices with touchscreen).
- Windows Smartphone 2003 (devices with keyboard and no touchscreen).
- Windows Mobile 2003/2003SE (devices with touchscreen).
- Windows NT/2000/XP/Vista (desktops and notebooks).
It has a support of OSM built-in.
It is freeware and recently its author (in OSM wiki it is User:Vsevolod Shorin) asked for help and decided to make it open-source.