I had a 2002 Tahoe that I purchased new. It was equipped from the factory with analog OnStar. When they converted OnStar to digital, I found out that my Tahoe could not be upgraded to Digital. Although I had planned to purchase a new Tahoe in 2008, the loss of OnStar was an additional incentive for me to do so.
OnStar did tell me that since my 2002 could not be upgraded, they would be glad to give me an additional year of OnStar service at no charge if I purchased a new 2008 Tahoe.
My sister-in-law had a DTS that had analog OnStar (unsure of which year model) and she was able to upgrade it from analog to digital, and at a very small price, perhaps $25.00?
When I was negotiating the purchase of my XLR, the dealer and I were very close to agreement. Finally, I asked if the OnStar could be upgraded to Digital. They checked with the Service Department and found out that it could be. We settled on a price that included the update and the first year of service.
Although I don't drive the XLR very much, I feel more confident with the OnStar in the event of a crash or other emergency. I DEFINITELY feel better with the OnStar Service in my Tahoe, as much as I drive in it!