Policy for mobile dev accessing network

I am busy revamping my security policy to also include mobile devices accessing network resources. Does anyone have some good guidelines, tips, comments or know of things I should be aware of when trying to put something in place??

One example isusing Nokia communicators to access email on the company's network and the risk associated with this - but then again a laptop could also be probleatic - stolen, etc...

Any advise appreciated

Kind regards

Pieter