Since the Sharp IS01's phone functions don't work outside of Japan, turning off the cell radio is a good way to conserve battery life. Unfortunately, since the handheld clamshell is running Android 1.6, enabling airplane mode turns off all the radios . . . period. The option to turn on WiFi while in this mode is unavailable.
Fortunately, there is a very easy fix for this.
Just head on over to Android Market on the IS01 and grab a free app called Airplane Mode Wi-Fi Tool. It has a simple interface consisting of four buttons (Airplane Mode, WiFi On, WiFi Off, and Landed) but you really only need to use it once. In the Preferences menu, there are options to always keep WiFi on when in airplane mode or to allow it to be toggled, regardless of whether the app is being used. WiFi can actually still be toggled using the former setting, so that's what I use on my IS01.
Cell standby uses more power than always-on WiFi, so turning off the cell radio makes a big difference in how long the device can run between charges.
QR code below.