According to Verizon.. you can use your Verizon plan IF you change the plan to the "Family" plan or if you already have a family plan with Verizon. this lets you use your Shared minutes (FAMILY PLAN) with the Acadia and your cell phone. Hope this helps.. But you still will have the second number for the car ;D
I already had a Family Share plan, so it cost only $9.95 a month to add another line for the Acadia.
After doing this, I received an invitation from Verizon to connect my OnStar phone to their service....and it appears to say that there is 2 year minimum verizon committment and you must have at least 1 year of your onstar contract....else there is a $175 termination charge.
I will call verizon and check this out....because they did not discuss any termination fees or minimum committments. If I don't continue with onstar after the first year, and the Verizon requires Onstar, then the termination fee would be less than well received.