I have the same mirror in my '01 Suburban and it displayed "ICE" like that since new. It only alternates "ICE" and temp for a few mins after start up then reverts to constant temp.
The scoop on OnStar is that any vehicle prior to 2003 was built with analog cell hardware. The FCC let the carriers discontinue analog service in Feb of 2008, so everything is 100% digital. I fought with both GM and OnStar, and they are standing by their position that analog hardware is NOT upgradeable, but they offered me a free 1-yr subscription if I bought a new car...
Now vehicles 2003 through 2004/2005 (depending on model) were built with "digital capable" cell hardware, and CAN be upgraded by the dealer. The '05's and up were built with digital hardware.
As far as usefullness, I liked it back in '01 and had a subscription up until they cut it off this year. It was a great hands-free phone before Bluetooth became common, also the concierge service was helpful before handheld GPS systems were so inexpensive. Now I can do all that and more on my BlackBerry, so it's really redundant. I did use it once for roadside service and that was handy.
