I have put a SD 16 GB in my LG Optimus 2X P990, but it seems that the phone won't save on it. Is it possible to save/move apps to the external SD card? Or even set it to do it automatically? I have already formatted the SD card twice, and it still is not working properly.
Try App 2 SD, it should be able to move at least some of the apps.
To set it to automatic, you will need the android SDK (to use
adb). From here, those commands should work (worked for me on my Samsung Galaxy Ace):
Probes Android devices connected to the PC. Do this first to assure that the phone is being detected.
adb shell pm getInstallLocation
This results in a numerical value to state where the default install location is (0: phone, 2: external).
adb shell pm setInstallLocation 2
This sets the default install location to the external storage.