Soon to enforce PIN on smartphones, what will happen?

I am about to enforce PIN policies on our BES, and our OWA servers, for any mobile device attaching to our exchange server.  We do not issue devices, so they are not our properity, so the only way I can do this is by setting the policy on the BES and on Exchange.

My question is the actual mechanics of the process once I set the rules.  In other words, what will the users see?  Will the device show a warning that a pin must be established before it will allow connection to the OWA/BES server?  Or will is simply stop sync'ing until a PIN is set?

Thanks much