Just got my son a O2 Credit type card, linked to my phone. Its in my name, but its his name too, so helps him get used to these things.
Anyway, topped it up with his spend last night, by debit card. Message was "available to use immediately". He went to the cash til to look too, novelty and all that.
Same debit card transaction takes X working days to hit the credit card. How strange :-)