Not much time now, but just back in my office.
Fanvil phones here (but tomorrow I’ll try with yealink)
Not only a blind transfer preserve outside caller ID, but it is preserved also with attended transfer : My phone rings showing incoming caller id
I answer and transfer to other extension
My extension name/no is displayed
Colleague answers, I hang up , and colleague phone shows incoming caller ID
That’s all… no mods on Advanced setting (all pbx have the same).
That can only happen by means of connected line update. I’m not sure if FreePBX defaults to sending RPID or PAI, but if it does, the phone still has to respond to the one selected. When you hang up, Asterisk will send UPDATE (even if the call is not answered, as long as the phone supports it), or will wait until answer and send a re-INVITE, with RPID or PAI, as enabled, containing the updated number.
It might be that the destination that has problems doesn’t support UPDATE., so no update can happen until answer.
The secret revealed !
New Yealink phones come with Caller ID source for account X set to “FROM”
I usually use a template for yealink phones where for account X , Caller ID source is set to “PAI-RPID-FROM” instead.
This second setting allow remote CID to be displayed after a succesfull transfer, both blind or attended.
Fanvil phones come out of factory with “PAI-RPID-FROM” cid source.