Yeah, kinda. An ISP I once had an account with used a 1:1 NAT where each public IP was mapped to a private IP on the network. What this meant was, essentially, if you needed to play a game or something, your IP was invisible to you from within Windows. After going through their AUP with a fine toothed comb and finding nothing mentioned about bypassing the NAT, I set up DynDNS on my computer (I remember it was phishphreek that suggested it) and bypassed the whole damn thing.
I can't imagine any laws against it, but IMO it is a cheapskate way to give inferior service.