Basically the same here in Tallinn, Estonia. We just have a sign that says the area you are in, city center, old town, etc. You just text the area your in and your license plate number. You can either get a 1 hour permit, 6 hour permit, or just a metered one that charges you for the time you where there (you send another message when you leave and it just calculates how long you where there). Its not more expensive, same price as using the machines and its super easy.
I don't see why more places don't do this. Instead of running to the meter every hour to throw another quarter in the machine, just send a sms from wherever you are.