My understanding is that if a California resident signs up for a service with a company in Iowa that has no California presence, that becomes interstate commerce. According to the Constitution and case law dating back to the 1800s (largely established by mail order companies), California does not have the right to regulate interstate commerce. Even when one end of that transaction is in California.
That is, in fact, at the heart of the whole sales tax issue with Amazon that has been in the news. By California state law, sales tax is owed, but California can't regulate what Amazon, an out of state company, does. Only Congress has that authority. (It looks like they may do it as well.)
I am not a lawyer, and could be wrong. If you want actual legal advice, you need to consult a lawyer. But this is my understanding.