How to drop out of airplane/flight mode periodically to check messages I normally keep my phone in Flight Mode (called "Airplane Mode" under 2.2) in order to save battery power.  When I have some time to check messages, I turn off Flight Mode, re-enabling the cellular transceiver.  Is there a way I can set up my phone to momentarily drop out of Flight Mode periodically, say every 10 minutes, preferably without using a non-free app?

I don't really need it to be in Flight Mode per se, just to disable power-draining devices, especially the cellular transceiver.
There are multiple automation tools which most likely can do this for you. Some of them, especially in connection with your real concern, are listed in my answer to What is Cell standby and how can I keep it from eating my battery?.

Aside from that, and you might wish to check helpers like JuiceDefender, Easy Battery Saver, and GO Battery Saver &amp; Widget. Amongs others, they do exactly what you asked for: toggling airplane mode or rather the data part of it, to enable apps to sync only in defined time frames.