I haven't owned an iDevice in some time so I'm not sure about the fine print (or even the bold print for that matter) but if the warranty terms do not explicitly prohibit or limit the number times a person can transfer a warranty or return a still in warranty device, then I don't see how they can bring a ton of charges with out looking like total douches. The proper course of action would be to issue an amendment to the warranty terms to change the policy. Then they have something to point to. But just having some random "nice uncle" lawyer make a call and intimidate the kid into submission is a pretty douchey thing to do.