Your 2000 Tahoe, if I remember right, came with an Analog Only OnStar system and when OnStar switched to a digital system, they probably just unplugged it since it was not able to be upgraded.
#06-08-46-007A: Information on OnStar Analog-Only Systems - (Sep 22, 2008) Subject: Information on OnStar® Analog-Only Systems Models: 1996-1999 GM Passenger Cars and Trucks Plus: 2002 Buick Rendezvous 2000-2003 Buick Century, Regal 2000-2005 Buick Park Avenue 2000-2001 Cadillac Catera, DeVille, Seville 2000-2002 Cadillac Eldorado, Escalade Models 2000 Chevrolet Impala, Lumina, Monte Carlo 2000-2001 Chevrolet Blazer, TrailBlazer Models 2000-2002 Chevrolet Suburban, Tahoe, Venture 2001-2002 Chevrolet Silverado 2002 Chevrolet Avalanche 2000-2002 GMC Denali, Denali XL, Jimmy, Yukon, Yukon XL 2000-2001 GMC Envoy 2001-2002 GMC Sierra2000-2001 Oldsmobile Bravada 2000-2002 Oldsmobile Intrigue, Silhouette 2000-2002 Pontiac Montana 2001-2002 Pontiac Aztek 2000-2003 Pontiac Grand Prix with OnStar® (RPO UE1) -------------------------------------------------------------------------------- This bulletin is being revised to update the models affected list above. Please discard Corporate Bulletin Number
06-08-46-007 (Section 08 -- Body & Accessories).
-------------------------------------------------------------------------------- All vehicles equipped with OnStar® listed in this bulletin were built with Analog-Only OnStar® Hardware. OnStar® equipped vehicles with analog-only equipment were designed to operate only on the analog wireless network and cannot be upgraded for digital network compatibility. Vehicles with this equipment will no longer be able to receive OnStar® services beginning January 1, 2008. At that time, service will be available only through Dual-Mode (Analog / Digital) equipment. Analog-Only vehicles cannot be upgraded to digital equipment.