As far as I know WDL doesnt own any A319s. They always buzz around in those old Bae146s and F27s. If the contact is in Zürich, then it might be PrivatAir who are leasing the aircraft to WDL. PrivatAir owns 4 A319CJ and A319LR and they are based in Switzerland. Most of those aircraft operate between Europe and the States on behalf of Lufthansa, but in PrivatAir colours.
Other than that it might be G5 Executive, Execujet or maybe even Jet Aviation who have a finger in the pie. All have bases in Zürich, but my bet would be PrivatAir.
http://www.privatair.ch/home.html