I'm wondering if there's any way to disable the calling features

Question

I want to write an app so that I can hand my phone to my 18 month old son and not worry that he'll make phone calls to my contact list.

Simply putting the phone in airplane mode is not effective because when he attempts to dial a number he gets the dialog asking him if he'd like to exit Airplane mode to make the call, which he promptly does.

It looks like I can't intercept calls coming in or going out, so, am I overlooking something or is it really not possible to put the phone into a state where it can't make calls?