I had a he/she apply for work years ago. I couldn't tell, and before anyone gets their panties in a bunge, it didn't matter. It just was puzzling, as the op realized also. Now you might think that I could have figuerd it out from the name. No go, it was Bobby. I couldn't even tell if the "y" was really a "y" or an "i" from the application. Even with a discussion during the interview, I couldn't tell from the voice.

I use ma'am and sir a lot and was at a loss. In the end, the person wasn't as qualified as other applicants and didn't get the job.

dl