In retrospect, I should have requested a carol on the Dial-A-Carol hotline this morning that was easier to sing. The caroler on the phone pulled up the lyrics of "O Holy Night." She apparently wasn't familiar with the melody, so she attempted to improvise. That hadn't happened when I'd called in previous years, but with so many calls coming in, I don't blame her for making that judgment call.
Later that afternoon, I called again, resolved to request a more familiar carol. Per my request, the caroler sang "Silver Bells," with a backup singer chiming in part of the way through it. Those carolers didn't let any pitch limitations in their singing ranges stop them as they forged ahead.
Due to a limited singing range, I've never sung Christmas carols to anyone over the phone. I commend all of these singers I heard today for giving my requested carols the old college try.