Doesn’t work.
An iPhone (without sim) cannot use FaceTime or iMessage. An iPad can. This is a huge advantage for a young child you don’t want to have a sim yet, but you do want the ability to keep in contact with. Stupid Apple decision.
The iPhone only needs a valid SIM to use FaceTime and iMessage; it doesn't, as far as I know, need an active SIM. Any valid SIM (that is, any SIM the iPhone isn't prevented from using due to a SIM lock), even one that no longer has service associated with it, should work. And once the iPhone is activated, the SIM can be removed and iMessage/FaceTime will still work, just (of course) not with a phone number.