According to the report, the new models will be dual SIM, dual standby. That means that both SIM cards are on standby when neither are in use. But once one SIM becomes active, the second one is inactive.
If you subscribe to the "where there's smoke there's fire" club, you probably would expect to see Nokia's dual SIM Lumia model before you would see one from HTC, which has its own set of difficulties to work out. Still, a Nokia Lumia dual SIM Windows Phone is not expected to hit the market until next year.
source: WPDang (translated) via WMPoweruser