1. Reboot (hard reset). Hold down the sleep/wake and home buttons simultaneously for roughly 15-20 seconds, until the screen powers off then an Apple logo appears, which signifies a reboot. Some problems may require (oddly) that this procedure is performed twice.
2. Reset all settings. The reset may restore disengaged hardware components and clear corrupt data that prevents proper connectivity. Navigate to Settings > General > Reset > Reset All Settings. Note that this will erase stored messages, passwords and other information.
Failing the above, try these battery saving tips.
1. “Reboot (hard reset)” works occasionally for me.
2. “Reset all settings” did not work. I tried once.
3. “Restore, but not from backup”. It requires updating firmware without ability to roll back on 3GS. I don’t like to have new bugs from Apple any more….