The OnStar system combines the features and services of the Global Positioning System (GPS) and Cellular/Mobile telephone/data networks, first developed in 1970s and deployed in 1980s.
OnStar originally used the Analog Cellular network (800 MHz, AMPS) in the United States.
OnStar migrated to the Digital Cellular network (800 MHz, CDMA),
as most of the original AMPS network was turned off in the United States on Febuary 18, 2008.Today, GSM and CDMA and their derived follow-ons are the predominate networks.http://en.wikipedia.org/wiki/Advanced_Mobile_Phone_System
The GPS Receiver in your automobile operates in the "L-band". There is NO transmit capability in this GPS usage band.
L1 1575.42 MHz Coarse-acquisition (C/A) and encrypted precision (P(Y)) codes, plus the L1 civilian (L1C) and military (M) codes on future Block III satellites.
L2 1227.60 MHz P(Y) code, plus the L2C and military codes on the Block IIR-M and newer satellites.
L3 1381.05 MHz Used for nuclear detonation (NUDET) detection.
L4 1379.913 MHz Being studied for additional ionospheric correction.
L5 1176.45 MHz Proposed for use as a civilian safety-of-life (SoL) signal.
The Sirius / XM satellite radio in your automobile operates in the "S-band" frequencies.
These services were allocated 25 MHz of bandwidth in 1990s, with rollout of services in late 2001.
The Sirius/XM service is received from satellites in Earth orbit as well as Ground transmitters in heavy populated areas (skyscrapers or terrain that would block the satellite signal).
Sirius Radio: 2,332.50 to 2,345 MHz
XM Radio: 2,320 to 2,332.50 MHz
Amateur Radio has frequency allocations at 1200 MHz, and shared allocations (ISM) at 900 MHz and at 2,400 MHz adjacent to WiFi
802.11b computer networks.
Despite attempts by Japanese radio manufacturers in early 1990s to expand US radio amateurs into these allocations .... majority of USA amateurs did not move to the microwaves (> 1 GHz) with the larger radio communications and computer network industries.
Antenna manufacturers have largely moved their new product manufacturing to 700 MHz and higher frequencies.
Commercial VHF/UHF products are historical artifacts of the 1950-1980 development period.