In all honesty, I don't really care to think that someone else can hear me peeing. Without my permission, a stranger had decided to send the sounds of me using the restroom out into the ether and share it (as background noise) with her friends.... and all because she can't be bothered to put her conversation on hold for the 5 minutes it's going to take her to take care of her restroom needs.
I wouldn't mind, I think, if I was in the restroom, someone's phone rang, they answered it, and you could tell from the conversation that it was an important, not to be missed call.
But, I think it's rude when a woman (or man, though I use the women's restroom) enters the restroom using her Bluetooth to "chat" to her friend about casual conversation ("Oh, we're thinking about going on vacation next Spring! Maybe you could go with us?"), continues the conversation throughout her whole restroom visit, and leaves the restroom still carrying on her conversation. In the meantime, she's broadcast the sounds of not only her own bodily functions, flushing, and handwashing but mine as well.
Not only is it rude to her friend but it is rude to me.
Personally, I think that some people are so "connected" that they aren't making good connections, if you KWIM. I always have to wonder about the people I see at restaurants who are ignoring their tablemates while they "chat" to friends on their cell phones, for instance.