You can convert from WGS84 to Web Mercator with esri.geometry.geographicToWebMercator.
Thanks, with this JS-Code all things are fine:fs=FeatureSet[PHP] $.each( fs.features, function(k, v){ point=new esri.geometry.Point( v.geometry.x, v.geometry.y, new esri.SpatialReference({ wkid: 4326 })); point_merc = esri.geometry.geographicToWebMercator(point); v.geometry.x=point_merc.x; v.geometry.y=point_merc.y; });[/PHP]