Avaya Index switch
I have various documents on Avaya's recommendations regarding the roadmap for the INDeX platform and the recommended migrations to either IP Office or Communications Manager.
The INDeX platform is a quality call centre system, the 400 model is a smaller system and would of been considered as ideal for your operation. Avaya have confirmed that as of the end of life, which is widely believed to be scheduled for November or December this year they will continue to manufacture parts for 3 years.
This means if you move your INDeX switch over to the new call centre you could face issues further down the line, but not in the near future. You will also only be able to get current functionality up to software release 11 as there is no planned development.
The CM3 or Communication Manager platform from Avaya would give you much improved functionality and would probably be Avaya's recommended path, depending on the size of your contact centre/operation.
There are many questions to be asked/answered and we held a seminar last week to discuss this vary subject, maybe I could send you a CD copy of what was discussed!
The next seminar is unfortunately not until Sept, which I doubt fits in with you timescales. There are lots of questions to be answered and various options for you moving forward, regarding investment protection, if you could email me directly we could assist you.