If you've been holding off on picking up a BlackBerry Passport Silver Edition until it was available for purchase through Amazon, your wait is over. The device can now be ordered through the online retailer in the US for $549 and you could have it as early as August 7, assuming you're an Amazon Prime member.
Something to be aware of though when ordering from Amazon is the fact there's no accessory bundle available, which includes the Passport Silver Edition Sync Pod, Flex Case, and Leather Flip Case, You will only be getting the device itself. If you're not interested in any of those items, though I can't imagine why you wouldn't be, hit the link to order the BlackBerry Passport Silver Edition from Amazon.
PS: Since people keep asking, keep in mind it's for GSM networks only. There is no support for CDMA networks such as Sprint and Verizon.