If you then notify the state that they have your money (such as via http://ucp.dor.wa.gov/ ), then you can file a claim, and they'll give you the money.
Phone cards are basically just (small) deposit accounts that are withdrawn against for one particular purchase. It makes a lot of sense that they'd fall under the same law.
Your "slippery slope" example on the other hand doesn't seem to match, because ISPs charge a fixed price for daily access. They don't (currently) take a deposit and then debit that account based on usage. If they did, then it seems like it might fall under the same laws.