James may come up with a more elegant option that doesn't involve any extra installations. In the meantime, I just tried the following solution, which works just fine with my old T-mobile Android, if you don't mind texting your phone.
I installed the free "Where's My Droid" app on my phone:
http://wheresmydroid.com/. The app does the same thing as Android Device Manager, so even if your phone is on silent it will ring at full volume or use a custom ring or siren, depending on how you configured the app. (It also has some other features.)
To locate the phone you can text it a special "attention word" that you've set up within the app. (You can also log in to their website and send the special code message from there.)
Depending on your carrier, you can often email an SMS message to the SMS Gateway, which means we can use the SMTP actions within VC.
The following simple command worked with my phone, no issues. My special attention word here is "Ring me":
<?xml version="1.0" encoding="utf-16"?>
<!--VoxCommando 2.0.0.0-->
<command id="297" name="Where's my phone" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>TTS.Speak</cmdType>
<params>
<param>Locating phone.</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>SMTP.Send</cmdType>
<params>
<param>[mycellphonenumber]@tmomail.net</param>
<param />
<param>Ring me</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<action>
<cmdType>TTS.Speak</cmdType>
<params>
<param>Message sent.</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>Where's my phone</phrase>
</command>
You would need to know the email domain for your provider, though. I'm not sure they all have them nowadays. Here's one reference list:
http://martinfitzpatrick.name/list-of-email-to-sms-gateways/