I think you have two options, assuming that all WM 5/6 phones use PAN:
1. Use the maemo-pan package (I think it's in the maemo.org downloads site. If not, search here).
2. Install DUN software for your phone (Never tried this but I think it's documented on the wiki here somewhere)

If you upgrade to Diablo, there's a bug that requires a few extra steps to use a PAN connection. Nokia is working on a fix.