I <3 my cell phone, its pulled me out of so many jams XD Yeah its extremely rude to have it in a playhouse or movie theater, I mean shit, you went to watch a show/movie and should be focused on that (unless you took a lady friend) so I mean seriously. Its why I love Hugh Jackman, hes an increadibly classy guy and doing what he did (even though he shoulda had the person kicked) was extremely patient on his part.
As for texting with friends, I can multi-task, but if a friend feels its rude, ill tell the other person im corresponding with that I'm busy and stop texting at that point.