Pros
You don't have to be very good at what you do. Avaya is a place where you can work (or not work) as much as you want as long as you are there the required number of hours per day. It's almost impossible to get fired, especially if you are one of the union workers. You can treat customers as badly as you like, ignore their issues and provide incompetent services and not have to worry about getting fired.
Cons
Management is focused on sales and not product development or personal development. Raises will not keep pace with inflation and you will never see any bonuses, even if they are promised. You will be surrounded by a bunch of people who hate their jobs which will translate into poor job performance thus making everyone's job even harder. There will be practically no training opportunities.