Bluetooth OBD

I have a 2011 Volt. Quite a while ago I read somewhere that if you use a bluetooth OBD device and leave it plugged in all the time, you will not be able to use Onstar as far as vehicle status and/or remote key fob commands. Is this true? Something about the car can only use one communication device at a time, like OBD and Onstar. I do have an Onstar subscription so I can get charging status updates and start my car remotely, I live in Phoenix and is nice to start it 10 minutes before I leave work.
If I can use both Onstar for the above mentioned features AND an OBD device, which android app is the best for monitoring the Volt systems?
Thanks