Imagining Avaya goes the way of Nortel, we'd be very inconvenienced.
We did a vendor dog-&-pony show with Cisco, Nortel, and Avaya about ten years ago, inviting them to set up a pristine and perfect demonstration phone center in our facility. We let them know we'd have our operators and call center staff come through and test/try/evaluate the performance and features of the systems, and the customers would rate how well their telephony needs were filled by each vendor.
Surprising to me, Nortel failed miserably. I say "surprisingly" because we were a 100% Nortel shop at the time, and their VoIP handsets and video telephone should've had the advantage.
Cisco came in second, according to our customers, which was also a surprise since they had top folks and perfect presentation and fancy cosmetics & bells & whistles like crazy. Of course they were also 200%+ more expensive than Avaya, and 300% higher than Nortel.
Most surprising to me was when our customers fell in love with Avaya's styles and feature sets and easy learning curve. I'd never heard of Avaya prior to this (of course, I wasn't in the telephony support business at the time, so perhaps I might be excused for this lack).
Since adopting Avaya we've retired old Nortel and Siemens phone systems with satisfaction. But we've also merged with smaller corporations that use ShoreTel and MiTel phones, and we've had a brutal time getting them to work with our Cisco security policies. Worse, some of those brands handle extended loss of site power events very poorly, hanging their PC's that run through them to the network. There've been a world of pain points with both of these vendors, and I can't recommend them from personal experience.
Cisco phones are probably the most expensive way to go, and despite them being the same vendor we use for most of our Network hardware and many Security solutions, I don't know that they are part of the solution for reducing the high cost of health care. Especially with all the power upgrades required for the POE needs of VoIP in general. I have a project on the burner from last summer where 4000 new VoIP phones were going into one of my facilities, and there was nowhere near enough POE to provide them all power, despite having 100% POE switches. It will cost $1.5M for the Maintenance teams to upgrade the 208 power and generators and UPS's in that facility. Or, the Communications team could spend $300K in 120V handset power injectors for the phones. Neither is a happy solution. Would it be better with some other VoIP product--unlikely.