Hi Dan,
As you can see, I've moved your new support request into its own thread on a more appropriate board with a more appropriate subject heading. Please try to follow this convention. Support buried in threads with meaningless titles are less helpful to other users.
With regard to your question: James explains the general principle for how to figure out this kind of thing here:
http://voxcommando.com/forum/index.php?topic=1435.msg12440#msg12440Basically, every addon is different and so there's no one rule, so you'll need to experiment.
Using the method described in James's post, we were able to get to "Live TV", from which you can use the standard navigation commands to select a particular channel.
<?xml version="1.0" encoding="utf-16"?>
<!--VoxCommando 2.0.0.8-->
<command id="821" name="U.S. T.V. live" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>XJson.Raw</cmdType>
<params>
<param>GUI.ActivateWindow</param>
<param>"window": "video", "parameters": ["plugin://plugin.video.ustvnow/?mode=live", "return" ]</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>U.S. T.V. live</phrase>
</command>
It may not be possible to create a command to play a specific channel because it looks as though a temporary URL is being generated.
We were able to get this to work as well, using the same method of looking for the correct syntax in XBMC's favourites.xml file, but you'd have to test the command over time to know whether that URL will continue to be valid. Seems unlikely, but who knows.
<?xml version="1.0" encoding="utf-16"?>
<!--VoxCommando 2.0.0.8-->
<command id="825" name="Play N B C" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>XJson.ExecBuiltin</cmdType>
<params>
<param>PlayMedia(rtmp://lv9.ustvnow.com:1935/dvrtest?key=[yourcustomURLcontainingyouraccesskeyinfohere])</param>
</params>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>Play N B C</phrase>
</command>