QuoteFirst, is my expectation about the Obi110 hanging-up immediately correct - is this what the device should be doing?
Yes! Within 2 to 3 seconds.
QuoteSecond, are there other settings that need to change to get this working?
The only relevant settings are those in Physical Interfaces -> LINE Port -> PSTN Disconnect Detection.
Here's the relevant quote from British Telecom info:
British Telecom CPC duration may be between 90ms and 130ms.
British Telecom Disconnection Tone is a minimum of 3 seconds 400Hz at -30dBm.
The settings that work for me are:
DetectCPC - enable
CPCTimeThreshold - 100 (you could try as low as 90)
DetectDisconnectTone - enable
DisconnectTonePattern - 400-30;3 (you could try 400-30;2)
All other PSTN Disconnect Detection settings disabled.
Are you using a BT line? I used to use Virgin Media and I know they inherited a real mix of exchanges from the various original cable companies. Many of these used different methods for PSTN disconnection detection.