I tried the iSimple and BlueStar CoStar bluetooth modules but I was not happy with the sound quality, reliability as well as they interferred with flashing my ECM.
I've done several of these VCIM installs on GMT-800 & GMT-900's and they all worked flawlessly with great sound quality. They use the factory OnStar mic and are easy to use but not so simple to install. The OnStar module with Bluetooth for the GMT-800 trucks that work are out of 2009 GMT-360's ( Trailblazer, Envoy, Rainer, Saab 9-7x etc.) I bought mine on eBay for under $100. You need to have the VCIM Module and Bluetooth Antennae
GMT-800 VCIM Part Numbers
25965167
20782641
20830941
20850446
22829371
Bluetooth Antennae 15938939
GMT-800's are not such an easy install as you have to take a fair amount of the dash apart and make a bracket to install the new module in the factory location behind the glove box and airbag. If you want to try it out before taking the dash apart you can disconnect the two connectors from the original OnStar module and feed them down to the passenger foot well and connect the new OnStar Module. I left mine this way until my wife complained too many times about kicking it.
GMT-900's are a much easier install and you need to have the VCIM Module, Bluetooth Antennae and steering wheel controls wiring harness. I installed it on a 2007 NBS
GMT-900 VCIM Part Numbers
25990227
20787642
25990228
20787643
25984444
20783877
25984445
20783878
20787107
25851951 - Audio/Bluetooth switch/ steering wheel buttons
15938939 - vcim Bluetooth antenna
OnStar® (VCIM) Module) found in Models:
2009 Buick Enclave
2008-2009 Cadillac CTS, CTS-V
2009 Cadillac Escalade, Escalade ESV
2009 Chevrolet Avalanche, Silverado, Suburban, Tahoe, Traverse
2009 GMC Acadia, Sierra, Yukon, Yukon XL
2009 Saturn OUTLOOK, VUE
All Equipped With Gen 8.0 OnStar® (RPO UE1) and Navigation Radio (RPOs U3R, UVB, U3U, UAV or UZR)
Issue with a used VCIM is it still have the VIN of the vehicle it came out of so if you use OnStar (I don't) they will call you by the previous owners name and reference the donor vehicle. However, OnStar will reprogram the VIN if you tell them your original VCIM died and you got a replacement.