I have an OBi200 and a BT Dongle, but only have made a few test calls and had no problems. Other than the test calls I never use it. I just did a forum search for "BT" in "Topic subjects only" and got 3 pages of hits. Some of the hit were questions and not problems. I'm guessing the vast majority of people don't have problems. You probably will have to purchase a BT Dongle to see if it will work for you.
You can configure the OBi200 to route calls to BT without the "**8" prefix. If you're interested, post back here after you get it working.