Seems to be some time when this thread was last addressed but it popped up when looking droid connection problems. Anyway, those are good solutions (airplane mode and reboot) to fix up problems related to lost connections but I would like to add one more. There's a widget available in Android Market that does pretty much the same thing with one-click-operation. Have a look if you're interested https://market.android.com/details?id=eu.versine.connectionfixer. I've personally found that useful and convenient tool several times already! 
