While the pre-orders have started now, there is no precise shipping date for either phone. Best Buy's website merely states that they will ship when available. Both manufacturers also have a mid-range model that has yet to price. The Nokia Lumia 820 and the HTC Windows Phone 8S should both turn up soon on Best Buy's site.
source: BestBuy via WPCentral
Best Buy and AT&T have priced both the HTC 8X and the Nokia Lumia 920 and pre-orders are being accepted