I see the following paragraph in the Asterisk trunk LICENSE file:
“In addition, Asterisk implements two management/control protocols: the Asterisk Manager Interface (AMI) and the Asterisk Gateway Interface
(AGI). It is our belief that applications using these protocols to manage or control an Asterisk instance do not have to be licensed under the GPL or a compatible license, as we believe these protocols do not create a ‘derivative work’ as referred to in the GPL. However, should any court or other judiciary body find that these protocols do fall under the terms of the GPL, then we hereby grant you a license to use these protocols in combination with Asterisk in external applications licensed under any license you wish.”
This probably originated some years ago, and I wonder if Digium or the Asterisk community might consider adding the OTHER management/control protocols to this list: ARI, and the ExternalIVR interface.
If not, it might be instructive to learn why!