The Nokia Lumia 800 comes in different variants.

HSDPA 900 / 1900 / 2100
HSDPA 850 / 900 / 1900 / 2100
HSDPA 850 / 1900 / 2100

Also the HTC Sensation has different variants.

HSDPA 900 / 2100
HSDPA 900 / 1700 / 2100
HSDPA 850 / 2100 (usually for Telstra AU or TNZ)