After you use your initial 130 minutes that OnStar gives to you at the introductory rate, it costs .40 a minute to renew. for a minimum of 100 minutes.
For this reason I linked my Onstar device to Verizon.
I get a family share plan of 1400 minutes a month, used on both my regular mobile phone and also with my Onstar device.
I pay $80 to verizon for my regular mobile phone, and 9.99 extra for the Onstar device #. I get all the same unlimited nights and weekends, as wit the mobile phone and just pay verizon. They also give me a new verizon phone # for the onstar device.
I do however need to keep the Onstar account active to utilize it. That is a seperate fee.