I don't mind texting..the tap tap tap is fine, really. Besides, I'm totally guilty of it too...as well as reading RSS feeds on gReader & checking Facebook when my phone gets sufficient signal. But thats different. The person you're texting doesn't need to know and won't know that you're camped out on the porcelain throne unless you tell them.
If you're actually calling someone, its hard to avoid the industrial strength toilet flushing going on in the background. If I were on the other end of said call, I would be disgusted. I've heard people arrange medical and dental appointments, their kids' early dismissals from school and just random personal conversations on the can.
Really? Do these people not see how disgusting and rude that is?!
Then again, I work in a place where people pee on the seat all the friggin time...in the ladies (obviously using that term super-loosely) room no less, so I shouldn't expect much, right?