Thank you for your replies. In checking the SIP messaging sequence, I saw that you are right about the source of the tag to the To-header: it is the phone, which as a response to the INVITE, adds the tag (and not, as I wrote, the FreeSWITCH). Still, we need a way to read it, and not the least to send NOTIFYs with the right tag. I have raised two issues on the Jira, maybe the category is wrong.

One of the tricky things to sort out is how to handle it in the case of bridging to a list of devices, and bridging to a user with multiple registrations. The NOTIFY method should include measures to send a NOTIFY to a specific phone among the many phones responding.

Thanks again for your excellent responsiveness – it adds the trust of the FreeSWITCH.   Jon.