Extension with no External Calling

This feature is not available, David. But there's an almost similar phone feature that might meet your needs. Go to our Support site at https://support.ringcentral.com/ and search for article Hot Desking Overview | RingCentral. To set it up, you need to contact your Account Manager.

hmm... but Hot Desking allows different users to log into a common phone.

I need this handset to be permanently logged in, but active only for calls to other extensions.

It sounds like this is not possible?

Must I buy a digital line, set for Hot Desking, with a dedicated user account? I do not need any outside calling.

Thanks,

ft.

PS. Extra info... the handset is on a production line, so line operator can make calls to internal supervisors, raw-material pickers, etc.

You would simply need to create a custom Role (depending on your version) and only enable "internal calls" in the policies tab.

thanks.

does this require a digital line?

Yes