Here's the contract manufacturer for phones sold by Altigen, Shoretel, Teleadvantage. Nice web site.

https://www.sayson.com/Default.htm

Hey Mark,
Sayson no longer manufactures the sets for Altigen. Altigen has designed and is manufacturing the IP sets. The latest is the
IP 710 and it is nice set.
https://www.altigen.com/analog-IP-telephone-sets.html

Good looking stuff.