In the early days of Onstar, it was a dealer installed option, but when they added the airbag deployment alert, and diagnostics, it has to be part of the vehicle. In fact, next year those 'old' Onstar systems won't be supported anymore, because they use analog cellular instead of digital, and that format is being phased out.
Current Ride 2015 GMC Terrain SLT
2nd Vibe 2006 Vibe AWD Stealth Monotone "Recon" December 2005 MOTM
Original Vibe: 2003 AWD Abyss Monotone "Darth"
GM/ASE Certified Parts Manager.
Ha!! I wish I would have gotten it... Many of the features are useless, however the other day I was riding in my friends Grand Prix that has it and the SES light came on, hit his onstar button to see if it was something urgent, and they were able to tell him that it was some sensor that could be triggered by a loose gas cap-- pulled over, and guess what gas cap was loose, light went off!!! Also, since it uses verizon's network you can now integrate your VZW cell plan and use your calling plan w/ onstar, which I find works much better than installed hands-free kits.Blah... too late now.