The purpose of this document is to provide acceptable proof to Customs that you own the mobile gadgets and did not purchase them while traveling outside the country. The alternative to obtaining this certificate is carrying around all purchase receipts for your mobile gear.
If you do not provide acceptable proof to Customs you may have to pay duty and/or taxes on your mobile gear, even though you did not purchase it outside the United States.
You must take all your mobile gear to your nearest Customs office with the completed form and present it for registration. Make sure you take all your mobile gear, even items you don't think you'll take this time, you might change your mind later.
Important Note:
Any repairs, upgrades or other modifications made while you were traveling must be declared and you will have to pay any applicable duty and/or taxes on those.