I am trying to understand whether it's possible to initiate a conference from a SIP softphone configured as an extension of Cisco Call Manager. As far as I understood from the documentation that I found on Cisco website, it's possible to initiate a conference from Cisco phone, but is it possible from another SIP UA? If it's possible, how can it be done? According to RFC4579, there are many ways in which a conference can be created. Which way is supported by Cisco Call Manager?