"The best business telephones in the world."

We just moved to a hosted PBX system with FreePBX (we had this as a local server...we just moved it to the cloud with a new vendor...same configuration).  We have 3 different locations (2 in Texas and 1 in Colorado).  All locations have different ISPs.  We also just implemented new ASA Cisco firewalls.  We use Snom phones and we have a couple of new Polycom IP6000s in our conference rooms.  Our Ft. Worth location is having issues.  The phone will not stay registered.  After a while ONLY the Snom phone will say "Prov. Server: Failed....."  We have checked with the hosted PBX provider and they say all is good on their end because the other 2 sites work just find.  The ISP says they're not a fault...they're giving us a wide open pipe with no restrictions.  The ASA router is configured the same at all the sites.  So...what is the problem.  Do you have any ideas??  Why do we not have a problem with the Polycom phone?  Does it use different protocols?  Your help is greatly appreciated.