Hi C. I'm also not aware of a way to do this via the RingCentral Admin portal. This programming would need to come from the actual endpoint phone. Unless RC professional services can maybe do something special.
What kind of phone are you trying to do this with?
Hello! RingCentral doesn't have this kind of feature yet, We'd love your suggestion added in our Ideas Portal. Please go to https://ideas.ringcentral.com/ and share your thoughts.
This can be done via the phone's web interface. You would open Notepad and enter this exactly: <test call.autoOffHook.1.enabled="1" call.autoOffHook.1.contact="10digitnumberhere" /> Do not change the formatting, simply add your number that you wish the phone to call when it is immediately off hook.
Save the file as .cfg, Utilities -> Import Configuration -> "Import" -> upload your file.
I did test this and it worked, you probably need admin access to the phone FYI (so bring your own phone or ask Ring Central tech support to try and do this for you). I did keep the <test in the code (thought maybe that was an accident but makes sense to me as well). I put this code at the end of the config file. My ending code is shown below, I was able to simply use a 5 digit extension as well (vs. a 10 digit number). I didn't heavily test to see if this could be worked around, with roles I restricted dialing. Enjoy and thanks for the great answer tak-it1 !!
reg.1.server.1.transport="TCPOnly" />
<test call.autoOffHook.1.enabled="1" call.autoOffHook.1.contact="12345" />
</PHONE_CONFIG>