"Unified Communication with [insert vendor here] will bring unparalleled productivity increases and reduced OPEX spending..... as long as you spend a butt load with us to start with and only ever use our product. Oh and you want to do this? Well you can't, here is a hack but it won't ever work properly. Sorry."
If all these companies didn't want to make money things would be so so much better. But they all think their propriety protocols are better than the RFC's.