we have a client who is using IP trade with Avaya but it was a very painful process for them. The go live was delayed 3 times and all in took 3 months for IP trade to get it working. I was not impressed with IP trades support there were several times I arranged for avaya & ip trade to be on site for a coop and they would not even turn up. They rarely apologised and even more rarely returned phone calls.
I would not recommend them but others may have different opinions, don't just listen to my (awful) opinion though.
"Anything that’s invented between when you’re fifteen and thirty-five is new and exciting and revolutionary, and you can probably get a career in it.
Anything invented after you’re thirty-five is against the natural order of things."