Anyway, many people could think otherwise, and sometimes the message conveyed may or may not change:
When I was driving she called.
I was in the middle of a trip and she made me a favour, she called someone else, at my request. BUT, it could be that when I was in the middle of the trip, she called me...
Fifty-fifty percent possibility here, I would say.
I was driving when she called.
I was driving when she called me OR I was driving and she made me a favour...but what someone would think at first, would be of the first possibility.
When I was listening to music she called. (in the middle of the activity of listening to music, she called? It could be.)
I was listening to music when she called.
The focus seems like in her calling me, by sheer coincidence I was listening to music. I could be doing the laundry, cooking, etc. The main event is that she called.