Polycom recommends that any customers who have already downloaded UCS 5.4.2 should download UCS 5.4.2 Rev D and use that release going forward.
If you have any questions, please contact your Polycom Global Support representative.
The Polycom 501's do have more and easier-to-get-to functionality than the GXP-2000's, and have a more professional look and feel (and a great speakerphone), but the most notable downsides of the 501 are its awful, obtuse and slow configuration interfaces.
Multiple 'stock' directories exist with different versions of SIP, UC, and Boot ROM software, and are named according to the SIP or UC software version contained within.
With the recent release of UCS 5.0 for Polycom VVX Phones automatic firmware updates are now supported directly from the Lync Device Update service.
I also don't go into pushing out configurations from XML files on a TFTP server, but it may be the way to go if you're doing more than one phone.
In the instructions below, TFTP is only really used to push out the firmware updates.