Since version 1.8.0 (Pro) and 0.34.0 (free) 3G Watchdog offers on devices with Android 2.3 (Gingerbread) a built-in mobile network enable/disable mechanism, compatible with the “Data enabled” aka “Use packet data” system switch (system settings > Wireless and network > Mobile networks > Data enabled) and with third-party applications using this switch to enable/disable the network.
This mechanism is proposed as an alternative to APNdroid and JuiceDefender in 3GW’s Auto-disable feature (3GW settings > Alerts).
Since 1.9.0 (Pro) and 0.35.0 (free) it is also possible to manually enable/disable the mobile network via the corresponding option in 3GW’s main screen menu. A widget (“Mobile data switch”) is available since 1.10.0.
Update: In Android 5.0 (“Lollipop”), Google in its infinite wisdom decided to make the built-in Android function inaccessible to third-party applications (only “system” apps can access it, that is Android apps plus apps installed by phone makers and ISPs on their branded phones), so the feature is no longer available. Alternative methods (APNdroid, JuiceDefender) are likely to not work either.
Google’s rationale for this decision is unclear, why shouldn’t/couldn’t a user grant a 3rd party app the right to disable the mobile data network on her phone in the first place?? If like us you are really unhappy with this decision that will deprive you of a very useful feature, please let Google now about your displeasure.