OnStar service will be terminated as of December 31, 2007 for customers who have analog only hardware. This consists of both an antenna, but more importantly the hardware module(*) in the vehicle. For the Bonneville, this consisted of 2 modules from 2000 - 2002 and 1 module from 2003 - 2005. The 2005 model year is already dual mode and doesn't require any change. 2003 - 2004 require an upgrade as the car is analog/digital ready. Prior to 2003 there is no upgrade available and OnStar service will be terminated at the end of the year.
There are a few GM lines prior to 2003 which can be upgraded but not the Bonneville. There would be no purpose in upgrading your antenna for the remaining two months you could have the service.
StingRay Bike w/cards in the spokes, Weeeeeee!