The new Maemo 5-based Nokia N900 Internet tablet has been officially announced and will be available for purchase starting this October for €500 (pre tax and pre carrier subsidy). Since it comes with 1700MHz band support, the most likely carrier to be selling it stateside is T-Mobile USA.
Nokia N900 specs:
Maemo 5 OS;
Quad-band GSM/EDGE, 900/1700/2100MHz UMTS/HSPA;
3.5" 800x480 pixel (resistive) touchscreen;
32GB of on-board storage expandable to 48GB via microSD;
5Mpix camera with Carl Zeiss optics and dual-LED flash;