As far as I know, that's because the Skype call isn't actually routed over the data connection, it transfers the voice via the existing voice network and the ot

As far as I know, that's because the Skype call isn't actually routed over the data connection, it transfers the voice via the existing voice network and the other end is hooked into a Skype gateway. [Citation Needed] but I don't have time to dig one up at work