Try this:
function GetOwner() { var owner = new Array(); owner = Xrm.Page.getAttribute("ownerid").getValue(); if (owner == null) { return; } var serverUrl = Xrm.Page.context.getClientUrl(); var oDataSelect = serverUrl + "/XRMServices/2011/OrganizationData.svc/SystemUserSet?$select=Address1_Telephone1&$filter=SystemUserId eq guid'" + owner[0].id + "'"; var retrieveReq = new XMLHttpRequest(); retrieveReq.open("GET", oDataSelect, false); retrieveReq.setRequestHeader("Accept", "application/json"); retrieveReq.setRequestHeader("Content-Type", "application/json;charset=utf-8"); retrieveReq.onreadystatechange = function () { GetOwnerData(this); }; retrieveReq.send(); } function GetOwnerData(retrieveReq) { if (retrieveReq.readyState == 4) { if (retrieveReq.status == 200) { var retrieved = JSON.parse(retrieveReq.responseText).d; alert(retrieved.results[0].Address1_Telephone1); } } } Bind GetOwner to whichever event is going to trigger