Windows Phone 7 users in Australia have so far been frustrated by the lack of local Bing support; the official Bing app does not currently return local listings, instead giving US-centric results. However, users have found a workaround that involves using region and language settings to return local results, as well as enabling the voice-search functionality which is also lacking from Australian handsets. WMPoweruser readers have reported that the workaround is functional, though it may not work for all users:
Note: This setting is OEM-dependent and may be limited or disabled in which case will have no effect. HTC devices seems to have this locked. LG and Samsung do not.
Thanks Zulu for the tip.