"I do hope the sound of your voice on that recording means I've reached the right number. This whole business of not needing an operator is rather odd. Miss Donovan, I wonder if you could meet me in the, ah, 'computer lab'. I require some help in matters of a technical nature, and since you've assisted in that capacity before, I was hoping I could call upon you again."

A pause that's slightly too long to not be awkward...

"...Goodbye."