Remove host (primary) headset and set it aside, turned off
Flip charging base over, and press and hold the mic volume up button on the bottom of the base. When telephone mode button on the front of the base begins blinking, let go
Now, press and hold the On/Off button on the guest (secondary) headset. After 5 seconds, it should start flashing
Set the flashing guest headset in the cradle
After up to 30 seconds, the blinking should stop. It's paired!
Remove the guest headset and make sure it turns on – Voila!
To un-pair the guest, simply resync it to its original base