I have a similar situation - my wife just upgraded and so we have a spare phone (Sprint/Samsung Epic 4G) that we'd like to let the kids use for games, videos, etc.
I want to ensure the kids (both under 10) cannot make calls, send texts, etc. But using games/wifi/internet/youtube will be fine since we do supervise them.
Is there anything I can/should do to lock down the cellular connectivity of the phone? Or is it incapable of making calls since Sprint activated my wife's same phone number on a new phone?
if it does not have an active carrier supporting it.. then it can not make calls. so it is pretty safe.
it can download skype (and other VOIP apps) applications.. and make calls on the data from your home wifi.
also they can make purchases from the Play Store...