I've just upgraded my phone from a SE T637 to a SE Z520a (Cingular). I'm using the phone with the BT/Assist 84-10-6-963-798 (9.2005) TCU. All works great and no issues to report ... however ....

The Yellow Lamp on the NAV unit is always lit as soon as the phone is paired with the car. With the T637, I only noticed the yellow light to come on when the phone was using a non-cingular network. This would make sense as the NAV Manual states that the indicator lamps for phone mode :

YELLOW: Telephone is being routed through alternate network.

So I'm not sure why I get a yellow lamp lit as the Z520a is definitly using the cingular network ... ?