[f5fstop]

Don't believe it can be done with the existing setup, and it might require a heck of a lot more than unlock codes. So let me be the wise ass and say you cannot do it for Cingular...with just the so-called unlock codes. Cingular does NOT use CDMA, Verizon does. Therefore, the internal circuitry of the VCIM is based on the Qualcomm CDMA technology, and is a Qualcomm board. (Cingular uses either GSM or TDMA, depending on the local system.)
As for your other company, I have no idea what system they use, but I will guess it is also GSM, since CDMA is primarily used in the USA/Canada.
GM owns Onstar, and they use the Verizon circuits with an agreement with Verizon. Verizon markets the use of the Onstar phone as part of their family network, and it adds business. Verizon also supplies about 90 percent of all GM issued cell phones. So, even if you had a CDMA provider in Mexico, why would GM give you this mysterious unlock code?
They do make handfree Bluetooth systems for automobiles.