Unhappy with relying on proprietary extensions to do the most trivial of enterprise features - hold, transfer etc - some vendors are tilting at the windmill to get interoperability going.
In this story by Phil Hochmuth of Network World, reports on the arguments for SIP-B (SIP for Business) , a definition of RFC 3261 extensions that could enable some proprietary extension conversions to standard practice.
Usually promoted by vendors with lots to gain, extensions to standards have a rough road ahead and the SIP-B, is no exception. In the story, Phil surveys the industry problem well (call transfer doesn't work if the SIP call control is from one vendor, and the SIP phone is from another). However, the fact that there is little industry support in IETF to codify extensions, and only a modicum of interest in the SIP Forum tells you that this is not a break-the-bank or kill-the-market impending feature requirement. It's a nice to have, with little benefit for the vendors who invested in their frameworks for proprietary extensions.
For all the years I worked for Nortel, it took Citel and 3Com to show me a phone system where a Norstar phone worked with a Meridian phone!