Even though we have a GMC, I trust that this question will stir some interest. The Sierra that we just bought does not have ON STAR. I have had and do have ON STAR in other vehicles and appreciate it very much. Here's the question: Can ON STAR be retrofitted to the 2015? I have read up on the ON STAR FMV units which are no longer made but are still available and would even use it if I could get some info on installation, etc. I understand that putting FMV into the Sierra would possibly negate the only feature that the current mirror has: automatic mirror "shift" due to approaching headlights from the rear. So, that's the question and I thank you one and all for any input.