The Mitel ATAs. They are model numbers 710X, where the X tells you how many analog ports they have.
The doco said something about them only supporting half as many fax machines as they have analog ports, but I got 2 faxes working together on a 7102.
You configure the Controller IP address as your "SIP Server", and the fax extension number as the SIP Extension Endpoint Registration.
Changes we made to the default config:
Enable G711u, disable G729, T38.
Change "Jitter Buffer" and "Behaviour on CED Tone Detection" to "fax".
The "WAN" port patches to your network and will do a DHCP request for an IP address. If you configure the ATA with a Hostname, it will register in DNS to make it easier to find.
The "LAN" port has a DHCP server running on it, so you have to make sure you disable that.
After you configure it, it won't work until you reboot it.