We called the number back: 937-229-3066. It IS the University of Dayton Alumni office. Why they're calling me, I have no idea. You can leave a voice mail asking them to stop calling you. Their message gives a lot of information about applying for a job as a "caller"--apparently, they are now hiring. They also give the name and number of the director of the alumni office.
Fellow UD alum here with intimate knowledge of how the UD fundraising apparatus works.
This phone number is 100% affiliated with UD. They do not use a 3rd party to solicit gifts...you probably know someone that worked in the call center while in school (UD Online in the late 90s, early 00s).
It doesn't matter if you've ever given or not, if they have your contact information they will call you asking for a "gift". Because you willingly supplied them your information (if they have it, you did) it doesn't matter if you're on the Do Not Call registry.
Their fiscal year starts on July 1, so if you plan on giving do it in July. That will save you a year of calls. I'm not trying to convince people to donate, but you can be very specific with your gift if you don't want it going to the endowment...specific scholarships, COC, athletics, etc.