Where's a good place for a quiet, private phone call in downtown Ann Arbor?

From time to time I need to go somewhere quiet for a phone call in downtown Ann Arbor. Naturally, the typical cafe scene with an espresso machine going in the background and piped-in 80s music doesn't suit as background noise.

Where's your favorite place to take a quiet call downtown? I'd gladly duck into a phone booth, if only there was one.