The volume controls on the TS iPhone App don't seem to be consistent and are very hard to set with a bluetooth device. If I'm listening through the speaker or headphones, I can usually control the volume. When I connect my bluetooth it is too loud and I have hurt my ears on multiple occasions. I even open the volume control within the TS app (where you can mute mic, set status away, etc) and the volume is all the way down - I can't turn it down any more.
I have an iPhone 4 and use the Jawbone ICON bluetooth.

These are the steps I have to take to get it to a manageable level and sometimes it doesn't work:
- I turn off the bluetooth (which then makes the teamspeak app too low to hear through the iphone speaker)
- Disconnect and shut down/close the TS app
- turn my ringer volume to about 75%
- open the TS app & connect to the server
- open the volume control in the TS App and turn the volume down
- turn my Bluetooth back on
- adjusted the volume (at this point, there is very little 'down' space to turn it down)

It seems like the app does not link to the actual volume of the phone. It is somehow independent - either that or it works based on the volume of the phone when you start the app and then becomes independent. If the phone is turned way down, the speaker volume of the app is barely audible and can't be turned up. You have to shut down the app, turn the phone's volume up and then reopen the app.
Just seems quirky!