I just tested Join.me successfully, using my laptop and desktop.
I was able to share the screen on my desktop, so that it appears ALSO on my laptop.
I also tested the free conference call function, by saying something into the microphone of my desktop computer. And I was able to hear my own voice from the headset on my laptop.
Since Join.me allows you to have up to 250 participants, you can basically give a teleseminar to 250 people.