I forget which Beatle said it (maybe it was George or Paul, I can't exactly remember), but one of them said that during Beatlemania, the only time they got some peace and quiet was in the bathroom. Remembering that quote is something that makes me wonder whenever I'm in a public bathroom and someone is on the can and talking on a cell phone.
There's a reason why "rest" is the word, restroom. Are you in a situation where you need a break from things, or you just need to relieve yourself? Go there. But I'm definitely not one to carry my business into the bathroom with me. Boundaries are good, no matter how good cell phone coverage is.
Still, it's weird to hear people conduct private phonecalls in a not-so private place. Do people really want to know what's going on at your job? Do you even care that people are listening to you talk about your job or what you want for dinner that night? I frankly don't want to hear that stuff, but what do I know? I'm always a little behind the times on things.