I have a stock Android 4.2.2 on Galaxy Nexus, so I think this can be related to all Android phones. When switching from 2G to 3G and vice versa internet connection is switched off for a few seconds, ...
When I disable mobile data in Android 2.2, the 3G symbol disappears. Does this revert my phone's signal to 2G? I don't want to lose my signal when I go to the subway, but I don't want to all my apps ...