Perhaps you can put it into Airplane mode. That will save battery and keep the phone portion off. And you can still turn on/off Wi-Fi with the pull down menu.
Mmm yes, I hadn't thought of that. It never occurred to me that you would be able to turn on wi-fi in airplane mode as surely you can then transmit data too? Anyway this does work.
So this goes most of the way to what me and the OP want, the ability to turn off the phone functions without taking out the SIM. So this will allow us to save the battery power while we are just using the device as a tablet.
However, it is not completely there. You cannot turn on mobile data in airplane mode - so the device cannot be used in 3G web browsing mode without the phone being enabled.
It is a good workaround though.
Much better, IMO, would be a simple toggle in the toggle (not sure what to call it) panel with the others (Wifi on/off, sound on/off etc) which enables you to turn the phone functions on and off too. This could perhaps be accompanied by a little red/green phone icon in the notification bar.
Another benefit of this would be to perhaps stop all those ***** reviewers of the FonePad who just say all the way through "but what an ***** you look with this as a phone", "what a stupid phone this size" etc etc. Please just ignore the phone functions and review it as a tablet WITH a phone as well for when you need it. This abaility to toggle the phone on/off would make it easier for these simple minded people to review it as a tablet!