These Onstar devices will also boost signal in a week area, but trust me they are not satellite. I have been in the cellular business on the switching side of the business for 20 years. Read one of my previous post or better yet go to the onstar site. Infact the service is provided by Verizon
http://solutions.vzwshop.com/onstar/
This is from the manual:
OnStar Information Page 37
Inoperative if Cellular Signal
Is Marginal or Unavailable
Since OnStar uses cellular technology for
communication with the OnStar Center, it can only
be operated in geographic areas where cellular
coverage is available. Although nearly all of the
North American population lives and works in
cellular coverage areas, there are various rural and
mountainous areas where coverage is marginal or
does not exist. Cellular service is also subject to
transmission limitations caused by atmospheric
conditions. OnStar service is only available in the
48 United States, Hawaii, Alaska, and Canada.
If a request for service occurs outside of these areas,
communication may not be available, and the
OnStar Advisor may not be able to help you.
Inoperative if Communications
Service Is Inactive or Inoperative
OnStar uses a dedicated cellular communications
service and will not operate if, for some reason, a
cellular carrier has deactivated cellular service.
Inoperative if Cellular System Is Busy
In any area, the local cellular system can only
handle a limited number of cellular calls at a given
time. Once volume has reached the maximum limit,
additional callers are denied access. If this situation
occurs when there is an OnStar request for services,
the OnStar system will automatically redial (a few
times for an OnStar service or indefinitely for an
Emergency button press).