Here's how to add a WMS service of a different projection such as 4326 to a basemap (102110):
var layer1 = new esri.layers.WMSLayerInfo({name:"1",title:"Rivers"});
var resourceInfo = {
extent: new esri.geometry.Extent(-126.40869140625,31.025390625,-109.66552734375,41.5283203125,{wkid: 4326}),
layerInfos: [layer1]
};
var lyr = new esri.layers.WMSLayer("http://sampleserver1.arcgisonline.com/ArcGIS/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/WMSServer",
{resourceInfo: resourceInfo,
visibleLayers: ["1"]
});
map.addLayer(lyr);
If you define the resourceInfo, you bypass the getCapabilities call that is executed when you use WMSLayer command ... this means you don't have to use a proxy page