I cant remember the passcode for my Plantronics 3xx headset

For all current Bluetooth headsets the passkey is 0000 (four zeros).
If the phone does not accept this code, please refer to your cell phone user's guide to ensure the proper setup procedure.

Note: Powering your cell phone off and on sometimes corrects this issue. You cannot change or personalize the PIN code/password of the Bluetooth headsets. It will always remain four zeros.

I have put the link for Explorer 200 Series User's Guide below which should be helpful.

http://www.headsetsdirect.com/pdf/explorer230_ug_en.pdf

Good luck from Headsets Direct!