 <p>With Bing Ajax 7 the QuadKey in not the only item provided, it also provides x, y, and levelOfDetail, a.k.a Zoom.</p> <p>Until I spotted this I too thought about a server side transformation, but it is available to you in javascript.</p> <p>Bing maps comes with x,y, and z that can be used for OSM web requests directly:</p> <pre><code>var map = new Microsoft.Maps.Map( &lt;snip&gt; ) function useZXY(tile) { return "http://tile.openstreetmap.org/" + tile.levelOfDetail + "/" + tile.x + "/" + tile.y +".png"; } var omsTS = new Microsoft.Maps.TileSource({ uriConstructor: useZXY }); var omsTL = new Microsoft.Maps.TileLayer({ mercator: omsTS, opacity: 0.5 }); map.entities.push(omsTL) ; </code></pre>