Major update for taking calls; alternative method that does not require repeaters.
If you already have your repeaters set up and all is working fine, and you don't have quality issues, just leave your setup the way it is. But, if you want to simplify or you're having issues, this is the way to go.
1. Install Virtual Audio Cables, and set at least one cable. Default settings are fine.
2. In RB, set "Input 1" Line in on the input settings tab to whichever line you set it to in VAC; in my case, and for this example, we'll be using a VAC cable I titled, "Line 2." For you, it may be "Line 1" or whatever.
3. Add a workzone if necessary by going to view/workzones/click the next higher number to give you a new workzone that will accept playlists, etc. Inside the workzone, click the plus sign and add an "AUX PLAYLIST."
4. As Dmitry said, when you set that "Input 1" to your VAC line, it will have added to your main playlist something like, "<SYSTEM> LINE INPUT" which you then just drag over to your newly created AUX PLAYLIST. Leave the settings for play times at 0 so it plays infinitely. Click PLAY (if you forget this, your calls will not come through nor your sound effects if you also use the following step I'm suggesting).
5. Set your Cartwall OUT device on the playback tab to whatever line you set your Input 1 Line in setting to; this will make sure your sound effects sync to your voice; playing them through the main output for me put the sound effects out of sync (this may vary depending on your connection speed, buffers, host, and system/setup).
6. Inside Skype or Google Voice, set input to MIC, disable automatic volume adjustment, and set output to the same line as your Input 1 Line in/Cartwall OUT are set to.
7. If you want to test the setup before going on air, you can call in to your Google Voice number (or Skype if you have paid for a number), mute your on-air mic, and just talk through the phone. You should hear what you say through the phone immediately with a tiny delay come back through your headphones, then you should hear it a few seconds later play back through your stream. If you don't hear your phone voice playing back, you have something set up wrong, so re-read 1-6. (Alternatively, if you don't have a skype number, you can make a test call in skype and you should hear the person who answers or the system voice come through your speakers if you are using Echo/Sound Test Service).
ADDENDUM (Ignore the following if it confuses you; just pay attention to the above). The following were the major advantages I gained doing it this way:
1. No repeaters are needed (VAC cable(s) or similar still is).
2. You can separate caller's voice from your voice so your settings don't affect his/hers (in my case, my co-host skyped in and I had line 2 and mic going to line 1, so with skype set to line 2 and me setting mic input to line one, my mic eq/comp settings also applied to him, and he had a great mic with awesome bass already so it completely slammed him into a wall, just about to blow out my speakers, sounded terrible).
3. If you are having sync issues with cartwall items, just set cartwall playback to whichever line you have set to aux input (I'm using VAC line 2, so my setup is aux input 1: line 2, and Cartwall playback: line 2). For whatever reason, that will sync your sound effects to your voice so they aren't out of sync.
4. It got rid of most of my popping/crackling (I still have main buffer set to something like 333ms; setting it to 75 gave me issues).