Yes, it is a SMS messaging icon.

I've had this on my US Bluetooth/Assist system as well. The thing is, BMW don't support SMS messaging on North American Bluetooth/Assist systems, so its odd that this icon appears.

I've only had this issue with a Motorola phone I had connected to the car. The weird thing was that the phone didn't have any sms messages (or any other messages for that matter saved, or new).

You cant go to the main telephone menu and scroll to "messaging", or SMS either as that option is not available.

So I concluded that it was just some odd bug, with this particular Motorola phone I was using !!

If I find out more I will let you guys know ....