DVR Shows needs to connect to your TiVo. For that to happen your iPhone (or iPod Touch) must be on the same network. When you are outside using your iPhone with a cellular connection or a different WiFi connection then you are on a different network from the one in your house. So there is no way to see your TiVo. And this is a good thing. Because if you could see into your home network from anywhere then so can anyone else.
However, there are some tricks you might be able to do with your home router that can expose access to your TiVo allowing you to run DVR Shows from anywhere. But this is an advanced setup that has nothing to do with DVR Shows. Another customer made this post:viewtopic.php?f=8&t=12
Since this kind of setup is done outside of DVR Shows and every router is a bit different I am not able to provide support with setting this up. But if you are able to make it work then DVR Shows should work just fine.