Thanks. well the whole sip-uri calling will be for most phones a problem, in the past i was also trying this, outgoing is a less problem, but incomming is the hard part,
You need a static IP address from your ISP,(or need a [external] DNS service) and this isn't normal in most cases.
Most of the time a firewall will block it, and the router at the receiving end should respond correctly, and then also for the xxxxx@ part, So i gave up on it at a certain moment, I guess not many people will use it, also because it is hard to set it up, for a normal user. (having a voip server would help, but is too much, for a feature like this)