OnStar (as implemented in late model Cadillacs) has a lot of new features that may (or may not) be compatible with the XLR.
Location Services offers the ability to download destinations directly to the Nav system remotely, using an app. I'll look up an address online, and send it to the car before I leave. Remote start on a cold or hot day is a nice feature that can be performed using the app, or the fob if its close enough. Not only does the car start, but the HVAC and heated/ventilated seats are functioning based on the outside temp. OnStar also provides a monthly diagnostic report. I can view the TPMS pressures and oil life indication remotely as well.
The MyCadillac app is nearly identical to the OnStar app (without the monthly diagnostic report) and includes an owner's manual. If the oil life reaches a certain threshold, it can make a reservation for an oil change at your designated dealership.
CC