Rover - that is the GPS receiver that is on the top of your tractor.  With RTK you have 2 receivers.  One is the base or fixed unit that does not move.  The second is the rover or mobile unit where you want to know the actual location.

I am not an expert on cell phone technology.  I have been told that low bandwidth data transfer actually works with a weaker signal than voice transmission does, but take that with a grain of salt.  I do not know if that statement is factual or not.  The Mojo RTK people have linked a cell phone booster several times on this site, but I don't find my book mark right now.  I remember that site making some pretty fantastic claims about range, but I have no person experience.  We do run external antennas on our cell phones and that seems to make a big difference.  But again, cell phone coverage is the key to making this work.

Mojo RTK has also said that their unit will be capable of directly receiving CORS transmission soon.  They have a cell phone built into their unit currently.

The Intime software is loaded on the phone to receive that CORS signal and pass it to the GPS receiver.  You are not making a phone call to get the signal.  The signal is on the internet.  The InTime software goes to the website and picks up the data transmission.  It then passes that data to the GPS unit.