Networking Partner™s, that is an interesting question! On the surface, the answer is no, but thinking about it further from CarGoSki's post, another idea just popped up. You might be able to use a DS1 to tie them, if the channels are configured as 4-wire E/M channels with Wink-start/DTMF options and 2-digit feed for the "DID" numbers, etc. from both systems. It would be a manual process, utilizing the pool feature to place a call to the other location. Some one that has two of these suitably equipped Partner™s would need to do a test setup to work out any bugs and verify the limitations, and operational processes, but it may be possible!
....JIM....