I think you need to make sure on your iPhone that messages are activated in notifications --- then in the iDrive you need to accept text messages (while in messages click on Options).
That's how I got mine to work. You can read them but you cannot reply to a message...at least I can't. I use iPhone 4
Current: 2015 BMW F80 M3
Retired: 2012 BMW 335is
Other: 2014 Mini Cooper