I've done this with my DH only, at home (and only because we're not in the same place so sometimes it can be the only call we'll have for a few days)! But I agree, it's really distasteful to do this in public - and weird!
It also seems too personal for even friends to do this! I have a friend who used to drive me crazy because she always had to tell me, "I'm taking you into the bathroom with me" or "I just went pee right now"!
TMI! If you absolutely have to go, and you cannot get off the phone (although I don't see why not), you should be as discreet and silent as possible, or cover up the phone at those "opportune" moments.
(I think it IS a much, MUCH more heinous crime to not wash one's hands with hot water and soap afterwards, however!)