Lync and Avaya, what does it say and what to do

Well Im back from Vegas and LyncConf. What a show, and those News. Just great.
At present time I'm out on job installing Lync 2013 for a customer. HLBA, 3 frontEnd, 2 Mediation and more.
They have and Avaya CS 1000 that shall be Integrated. I have checked out and Avaya is supported on Direct SIP, but as Microsoft say, this is at present time, and we don't know about the next versions of the Avaya software. So we would advise you to use an gateway.
Well, that was easy or was it.
To invest in a gateway for about 2500 users, well you need a lot of SIP lisences for the gateway. Shall the Gateway be part of the cluster og HLB.
How long shall Avaya live before we go for the SIP trunk Direct from a telco?
This is needs that we have to talk to the customer about.

As now we landed on to advise Our customer to go for the Gateway. I think there will be a Sonus SBC 2000 With dual Power......... More will come on this later :-)