Here's how the developer describes this new feature:
Cortanium will now have Cortana send you a "fake" phone call from one of 40 different people, and up to 200 will be added over the next few days. So, for example, you can tell Cortana to have "Elvis call me in 10 minutes" and you'll get a call from "Elvis"! This is not just fun, but a great feature in case you're in a meeting and want an excuse to duck out, you can say, wait, Bill Gates is calling me, I've got to take this call…and prove it with your phone!
Liquid Daffodil is currently taking requests from fans on which people they should add to Cortanium's fake call list.