Ahh, I'm not the only one missing that :-)
-> The ATA-186 is not supported with CUOM.
You'll find a (pretty useless) list of the ATAs on the CUOM here (afaik the only place where they are mentioned in the CUOM):
Reports / IP Phones and Applications / All ATA devices
I talked already with Cisco and this is the answer I got - please don't blame me for the content :-)
"The ATA-186 devices that you reference in your email lack any instrumentation in them. Hence, it is not possible for CUOM (or any other management software) to discover and manage it. CUOM however, can give you the status of the ATA port indirectly by monitoring the Ethernet port on the Switch to which the ATA is connected."
Cheers,
Martin