Plantronics 520 will not pair

"Begin with the headset turned off. Press and hold down the silver call control button in for 6-10 seconds. The light will flash blue first. Continue to hold the button down then release the button when the indicator light starts flashing red then blue."

The fact that the previous device is disabled should not matter.

1. Turn on both the phone and the headset
2. To put the headset into pairing mode, at the same time press the Call Control button (side of the headset) AND the volume button marked "+". When the status indicator light flashes between blue and red, you are in pairing mode.
3. Now use your phones menu to search for bluetooth devices, you should see it say "PLT 520" on the screen. Note, this can take up to 2 minutes.
4. When it asks for the passkey, enter "0000" (zeros). When the light on the headset turns blue you are successful.
5. If this fails, try again
6. If this fails again...reset the headset. To reset, do a long press of the MUTE and volume down buttons simultaneously for about 3 seconds, then try the procedure again.

This works; the secret is to continue holding the silver button after you hear the beep for the full ten seconds.

I just finally figured out that you need turn on the bluetooth on your phone so it is searching for a device. Then you need to hold the volume/power button down until it shuts off, then hold the button again to turn it back on and keep holding the button down until you see the red and blue flashing back and forth. At that point, your phone will find your device and you can enter the password which is usually 0000.