Amazon.com Inc trumpeted cutting-edge wireless technology as a key selling point for the fanciest of the new Kindle devices introduced by CEO Jeff Bezos on Thursday. There's just one problem: the devices have not yet been approved for sale by the Federal Communications Commission.

FCC approval is required for wireless communications products, to assure that they operate safely and won't improperly interfere with other signals.

A pre-order confirmation email sent by Amazon late on Thursday, September 6, for the $499 Kindle Fire HD 8.9-inch 4G tablet included the following note: "We will send you an email asking you to confirm your pre-order of Kindle Fire when it is approved for sale by the Federal Communications Commission."

Amazon is accepting pre-orders now and plans to ship the 4G devices on November 20. A company spokeswoman said Amazon expects to receive FCC approval before November 20.

Attorneys and analysts familiar with FCC compliance procedures agreed that the FCC is unlikely to reject the Amazon devices out of hand, or prolong the approval process past its ship date.

But they say it's very unusual for a company to announce major new products without first getting the sign-off from the agency.

"I can't think of an instance where a device has been offered by a U.S. carrier or an independent retailer that has not had FCC approval yet," said John Jackson, a wireless analyst at CCS Insight.

An FCC spokesman declined to comment.

The 4G Kindle Fire tablets are a crucial part of Amazon's attempt to challenge Apple Inc's iPad at the premium end of the booming tablet market.

The lack of FCC approval at this stage is likely a result of Amazon's lack of experience with wireless hardware, according to Charles Golvin, a wireless analyst at Forrester Research.

Lazarus said Apple Inc, Motorola, now owned by Google, Samsung and Microsoft have never had such issues.

"These companies have dedicated staff whose job it is to ensure FCC compliance and they do their job very well," Lazarus added.

Sprint Nextel, a leading wireless carrier, does not release phones for pre-order unless they have already been FCC approved.

"In the vast majority of cases, we will not accept a phone into our formal lab process that has not already received FCC approval," said Sprint spokeswoman Michelle Leff Mermelstein.

A spokeswoman for AT&T, which is providing the 4G data plan for the new Kindle Fire wireless tablets, declined to comment.

FCC rules bar marketing of devices that are not approved for sale by the FCC. However, there is an exception that permits advertising as long as a disclaimer is included in the promotion, according to Mitchell Lazarus, a partner at law firm Fletcher, Heald & Hildreth, who has 27 years of experience obtaining FCC approvals for new technology, including wireless devices.

Amazon's press release announcing the devices and the product description pages on the company's website include disclaimers saying "The 4G device has not been authorized as required by the rules of the Federal Communications Commission. This device is not, and may not be, offered for sale or lease, or sold or leased, until authorization is obtained."

"Most companies try to get the FCC work done before they announce new products, so they don't have to make these awkward disclaimers," said Lazarus.

Amazon may be waiting longer for FCC approval because the company engineered its own 4G wireless modem to be thin enough to slip inside the new Fire tablets, Forrester's Golvin said.

Bezos highlighted the new modem during his presentation on Thursday, noting it was 2.2 millimeters thick.

Most wireless devices have modems that have been used in other gadgets that have already been approved by the FCC, smoothing the process, Golvin said.

The other new Fire tablets unveiled by Amazon on Thursday only have Wi-Fi and those devices do not have the FCC disclaimer.

"That would indicate that this is related to the new 4G LTE modem," Golvin said.

Lazarus said companies cannot accept orders and payments from consumers and they cannot ship devices until they are approved. They can accept wholesale orders, but they are not allowed to ship products to retailers until they get FCC approval, Lazarus added.