I have a 2011 Chev Avalanche LS; was able to pair my iPhone 4 and then the iPhone 4S without any issues; worked great. (Yes, unfortunately past tense!)
A couple weeks ago, all of a sudden it started acting up on me. The handsfree wouldn't work - it started with a call coming through the iPhone only. I couldn't get iPhone to put the call through the vehicle's system. "General Motors" selection was available, but wasn't clickable.
I had already had a battery problem with the iPhone 4S and was having it replaced. New replacement iPhone 4S arrived a few days ago. Tried to pair it to Avalanche's Bluetooth. iPhone won't discover Avalanche's Bluetooth.
Tried connection with Blackberry Bluetooth earphone device - iPhone wouldn't discover it.
Tried to pair Motorola cellphone to Avalanches' Bluetooth - discovered once, but Motorola phone wouldn't allow input of 'passkey', so it didn't pair with Avalanche's Bluetooth. After that close connection, the Motorola wouldn't discover the Avalanche's Bluetooth.
The original iPhone 4S had the latest IOS 5.1.1 installed and worked great - but, it was paired back in Nov 2011, so the iOS would have been a earlier version.
Apple has offered to replace the replacement, though.
But, if we don't know where the problem is - then, I'll probably have the same issue with the new New Replacement!!!
I'll keep you posted!