Thanks, I thought it would be something like that but wasn't sure if i also needed a rule to block "in-interface=ppp-True3g" but i guess if the outbound traffic is being blocked, there shouldn't be any incoming traffic.
"in-interface" is not needed because your PS4 are behind NAT.
If with UPnP the PS4 open some ports on ppp-true3g, the ps4 can not comunicate to servers the port opened on ppp-true3g.
If the remote servers do not know the IP, "in-" comuication do not happen.
I'm Italian, not English. Sorry for my imperfect grammar.