I'm totally not an expert, furthermore I'm not a lawyer either... I just 
like this discussion.

So... (hypothetically) if it's legal for someone under the age of 16 in 
Montana to call a 900 number. Would it be legal for a 16 year old to 
call (from Arizona) a 900 Number in Montana?

Not that this is exactly the same thing...but we are trying to decide 
which laws take precedent.  I'm sure if you filled the complaint in the 
State of Arizona against a business in Arizona who was breaking Arizona 
Laws but doing it through another office in a another state, the case 
would still have precedent in Arizona.

Now if they counter sue you in Montana that will be left up to the 
Montana courts. Can they even counter sue from another venue? I would be 
willing to bet that they can only counter from the original state. But 
keep in mind you can sue anyone for anything. It's up to the judge if he 
will hear you or not.

 From all the T.V. that I've watch usually states don't mix their legal 
battles unless it's a really big deal.

Chris