--- a/dom/telephony/test/marionette/head.js
+++ b/dom/telephony/test/marionette/head.js
@@ -274,16 +274,28 @@ let emulator = (function() {
         return telephony.calls.length === 0;
       });
     });
   }
 
   /**
    * @return Promise
    */
+  function changeModemTech(aTech, aPreferredMask) {
+    return Promise.resolve()
+      .then(() => emulator.runCmd("modem tech " + aTech + " " + aPreferredMask))
+      .then(() => emulator.runCmd("modem tech"))
+      .then(result => is(result[0],
+                         aTech + " " + aPreferredMask,
+                         "Check modem 'tech/preferred mask'"));
+  }
+
+  /**
+   * @return Promise
+   */
   function clearCalls() {
     log("Clear existing calls.");
 
     // Hang up all calls.
     let hangUpPromises = [];
 
     for (let call of telephony.calls) {
       log(".. hangUp " + call.id.number);
@@ -1147,16 +1159,17 @@ let emulator = (function() {
 
   this.gDelay = delay;
   this.gWaitForSystemMessage = waitForSystemMessage;
   this.gWaitForEvent = waitForEvent;
   this.gWaitForCallsChangedEvent = waitForCallsChangedEvent;
   this.gWaitForNamedStateEvent = waitForNamedStateEvent;
   this.gWaitForStateChangeEvent = waitForStateChangeEvent;
   this.gCheckInitialState = checkInitialState;
+  this.gChangeModemTech = changeModemTech;
   this.gClearCalls = clearCalls;
   this.gOutCallStrPool = outCallStrPool;
   this.gInCallStrPool = inCallStrPool;
   this.gCheckState = checkState;
   this.gCheckAll = checkAll;
   this.gSendMMI = sendMMI;
   this.gDial = dial;
   this.gDialEmergency = dialEmergency;

new file mode 100644
--- /dev/null
+++ b/dom/telephony/test/marionette/test_modem_switch_tech.js
@@ -0,0 +1,54 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+MARIONETTE_TIMEOUT = 60000;
+MARIONETTE_HEAD_JS = "head.js";
+
+let settings = [
+  // "gsm/wcdma"
+  {tech: "gsm",   mask: "gsm/wcdma"},
+  {tech: "wcdma", mask: "gsm/wcdma"},
+
+  // "gsm"
+  {tech: "gsm",   mask: "gsm"},
+
+  // "wcdma"
+  {tech: "wcdma", mask: "wcdma"},
+
+  // "gsm/wcdma-auto"
+  {tech: "gsm",   mask: "gsm/wcdma-auto"},
+  {tech: "wcdma", mask: "gsm/wcdma-auto"},
+
+  // "cdma/evdo"
+  {tech: "cdma",  mask: "cdma/evdo"},
+  {tech: "evdo",  mask: "cdma/evdo"},
+
+  // "cdma"
+  {tech: "cdma",  mask: "cdma"},
+
+  // "evdo"
+  {tech: "evdo",  mask: "evdo"},
+
+  // "gsm/wcdma/cdma/evdo"
+  {tech: "gsm",   mask: "gsm/wcdma/cdma/evdo"},
+  {tech: "wcdma", mask: "gsm/wcdma/cdma/evdo"},
+  {tech: "cdma",  mask: "gsm/wcdma/cdma/evdo"},
+  {tech: "evdo",  mask: "gsm/wcdma/cdma/evdo"}
+];
+
+startTest(function() {
+
+  let promise = settings.reduce((aPromise, aSetting) => {
+    return aPromise.then(() => gChangeModemTech(aSetting.tech, aSetting.mask));
+  }, Promise.resolve());
+
+  return promise
+    // Exception Catching
+    .catch(error => ok(false, "Promise reject: " + error))
+
+    // Switch to the default modem tech
+    .then(() => gChangeModemTech("wcdma", "gsm/wcdma"))
+    .catch(error => ok(false, "Fetal Error: Promise reject: " + error))
+
+    .then(finish);
+});