changing Display Name during a call

[sergeysi]

Thank you for the answer, James.

Unfortunately INFO method did not work. Phone replies 200 OK but doesn't update info on the screen.

I finally had a success with UPDATE method and PAI header. But there are some questions. UPDATE method only worked with reverse tags in From and To headers (it means I had to place "From" tag to "To" header and vice versa). In this case phone answers 200 OK to UPDATE from PBX and actually updates text on the screen. But then phone replies "500 Server Error" to BYE from PBX.

There are 2 dumps attached:
update1.pcapng and update2-reverse-tags.pcapng differ only in From and To tags order. In update2-reverse-tags phone actually updates screen but replies "500 Server Error" to BYE from PBX. In update1.pcapng phone replies "481 Call Leg/Transaction does not exist" and replies coreectly to BYE from BPX.

What am I doing wrong? Why does phone accept UPDATE only with reverse tags and replies 500 to BYE?