Marquette University in Milwaukee has 11,000 students and 1,00 faculty and staff. As an independent university, they've got to make their budgets add up, so when they started to build three new campus buildings, they looked at the cost of the core services they provide - including their phone systems. What they did was replace their existing PBX phone system with a unified communications system - chopping their annual telecom costs in half, saving $120,000 a year.
I only know about this because of the story on the CIO Australia website, written by Shane O'Neill. There's detailed background about the decisions they took (and the alternatives they explored) to get them to where they are today - 1,000 staff using Lync as a replacement for their telephones, and adding audio & video conferencing, as well as instant messaging.
The full article is definitely worth a read, as one of the key elements is the key learnings that they made whilst doing the switch:
Read the full story on the CIO website