News to me, maybe some of you know this already. I'm usually WAY behind the times on most tech stuff:
Just got a 2015 Cruze diesel. Comes with the standard GM-offered 3 months of complete OnStar service. What I didn't know is that for 2014 and newer used vehicles you can get a "Basic Connectivity Plan" free for 3 years. You don't access it thru the little, blue OnStar button in your car but rather thru a cell phone app. So, when the 3 months runs out it reverts to the Basic Plan. No CC info required. Of course, when you push the button to sign up they'll try to up-sell you to paid plans but they weren't aggressive about it and it took about 5 mins.
Through the OnStar app you can remotely start/unlock your car, find it (horn and lights), get diagnostics, send a location to NAV system, etc... The link below will answer your questions. Seems like a pretty good deal to me.
OnStar Basic
Off Topic: My wife liked the little Cruze diesel so much we drove to Missoula, MT for one at a dealer there. She traded her Impala almost straight across. On the way back, over Lolo Pass and the winding mountain roads between Missoula and Lewiston (about 220 miles) the car averaged 52.6MPG! And I was in a bit of a hurry so I had my foot in it most of the way.