[SIP Beyond VoIP] discovering voicemail uri?

[Juha Heinanen]

in my blink account jh at test.tutpro.com server settings/extra server
settings/voicemail uri there is help text "Discovered by subscribing to
jh at test.tutpro.com".

i checked from RFC 3842 SIP Message Waiting and didn't find any means to
tell in message-summary notify what the voicemail uri is.  the notify
just contains the account uri.

how is blink expecting to learn voicemail uri of the account and has
this means specified somewhere?

-- juha