So every time I sneak into the tower behind Curtis, he NEVER talks on the radio. It doesn't matter if I go in right behind him or wait until 1 AM, every time I find him there he's just standing at the radio, staring ahead.

I tried waiting until the next day and pickpocketing the activation code from him, but since I never confront him, I can't get on the monorail and I can't go to Hsu with the info. So it seems until I hear that radio conversation, I'm pretty well stuck (or at least out of ideas). Any thoughts?

This quest has been bugged for me on every play through when I tried to save the monorail. If you have any saves before you triggered this quest, I'd say you should reload, but I never got it to work unless I was blowing it up.

On PC at least the quest works correctly. I've both saved and destroyed the monorail several times with no problems.

When you enter the tower after him your maybe being detected and halting his call ?
or
Entering to soon after him and being caught as he goes up the stairs ?
If its neither of them then maybe go back to a previous save and redo the quest.