OnStar Generation 9 Hardware
Chances are if you are reading this then you have interest in adding the OnStar MyLink Mobile App for iPhone and Android phones to your current smartphone, but you see a little astriks (*) next to your vehicle, telling you to contact your dealer to see if you have Generation 9 Hardware. Here's some background.

Generation 9
General Motors is currently using OnStar Generation 9 hardware which does includes enhanced services and diagnostics features and provides the ability to use the web mobile application, "OnStar Mobile App" called MyLink. This app allows subscriber to perform system functions, see OnStar diagnostic information, remote door lock & unlock, see the amount of fuel left in the tank, and more - all without needing to call into the OnStar center.

OnStay MyLink Functions: Functions include remote start, remote lock and unlock, flashing lights and horn as well as viewing up-to-date diagnostics data from the subscriber's iPhone or Android-powered mobile phone. OnStar hardware is currently manufactured by Continental AG and LG Electronics, although early models were made by Hughes for Gen 1, Delphi, for Gen 2 and Motorola for Gen 4 to Gen 6.
Analog

The Gen 1 to Gen 4 models were analog. All were for Class 2 bus. Gen 5 models were a transition period. Some Gen 5 models actually contained both analog and digital cellular phone modules. Also, there were both Class 2 and CAN bus models.
Digital

The Gen 6 and up models are CDMA digital. Some were Class 2 bus and some were CAN (Controller Area Network) bus.
Compatibility

Some Gen 5 and Gen 6 models were compatible with each other providing some upgrades to some customers to Digital. Analog cellular was turned off in Feb, 2008. Customers that had the Gen 1 through Gen 4 models were unable to upgrade to the Digital Gen 6.
No compatibility in Gen 1 and 4 with other models.

Some compatibility with Gen 2 and Gen 2.6 (Delphi TCU and Motorola cellular transceiver).

Page data comes from http://en.wikipedia.org/wiki/OnStar