Amazon's Kindle Fire HD 4G LTE tablets sales can't be finalized, and the device's United States release date remains in question, thanks to a lack of approval from the U.S. Federal Communications Commission (FCC).

While Amazon's flagship Kindle Fire HD tablet can't officially be sold in the United States yet - current pre-order customers will be asked to finalize their purchase once the Kindle Fire HD 4G LTE receives FCC approval - Kindle Fire HD 4G sales remain unaffected in the United Kingdom. A company spokesperson confirmed the Kindle Fire HD 4G LTE will begin shipping to UK customers on October 25, and Amazon hopes to have the FCC's approval to begin officially selling the Kindle Fire HD 4G to customers in the United States by November 20. Even wholesale orders, which can be accepted during this period, cannot be shipped until the Kindle Fire HD 4G LTE receives approval.

Forrester Research's Charles Golvin suspects Amazon's new 4G LTE modem is to blame for the delay, in large part because the Wi-Fi restricted Kindle Fire HD tablets have not been delayed as well. The new modem, which CEO Jeff Bezos debuted at Amazon's Kindle Fire HD press event last Thursday, crams 4G LTE power into an impressively small 2.2 millimeter thick package. But according to Reuters, there is no precedent for opening sales of a wireless device prior to its approval by the FCC. None of the industry's major players - including Apple, Samsung, and Google's Motorola division- have ever opened pre-orders for such a device in the past. Sprint spokesperson Michelle Leff Mermelstein also confirmed that her employers rarely consider phones "that [have] not already received FCC approval." A spokesperson from AT&T, providers of the 4G data plans that Amazon will offer Kindle Fire HD 4G LTE customers, declined to comment on the matter.

Amazon hopes to secure FCC approval in time to begin shipping the Kindle Fire HD 4G to U.S. customers on November 20. So keep your fingers crossed, and we'll keep you updated in the interim.