Call comes into extension 1. Should not ring extension 2. However, extension 2 needs to see the incoming caller ID so, if necessary, extension 2 can pick it up (using the feature code for Call Pickup).
Sorry I don’t know if there is a name for this, otherwise I would be able to search for it.
System is Asterisk 11.19.0 with Yealink 23G phones.
Knowing that another phone is ringing via BLF is usually pretty straight-forward, but getting the Caller ID information on that call is a LOT more interesting.
Essentially, you’d have to set up a custom-context for phone 1 that populates a hint and then display that hint’s value on the screen of phone 2. If you do manage to get it working, please post your code so we can see it.