iPhone - do not receive significant location changes in iphone 3gs with iOS 4.2

I am trying to execute the following code on my iPhone 3gs, with the OS version as iOS 4.2.1

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 40000
    [m_coreLocationMan startMonitoringSignificantLocationChanges];
#endif

It somehow does not work for me. It works on my iPhone开发者_如何转开发 4, but not on iPhone 3gs with iOS4. Does anyone have any insight into the problem?

Check the return value of +[CLLocationManager significantLocationChangeMonitoringAvailable]. If that says YES on the problem device but you're still not getting any messages, then you have a problem; otherwise, it's the expected behavior.