AMoonHawk saidIf someone is too busy to talk to me on a date and continually answers his phone, I order a very larger water then snag their phone and stick it in the water and leave
LOL! Well, you introduce the issues of dates, whereas the OP was talking friends. Maybe we can discuss both situations, which may have differences.
I think friends can be more tolerant of call & text interruptions, because they likely know your job & routine, and things often aren't as formal when you go out together. Still, it's polite to alert even your friends that you may be getting an expected call, and when it arrives to ask, out of courtesy, if you may take it in their presence, or excuse yourself.
As for dates, though, I think you answer your cell at your peril, especially first-time ones. The focus should be on him only.
Although I have been known to resort to a little cell phone theatre. Deliberately leaving the phone on, when a call comes I pretend I forgot to silence it, saying it can go to voice and wait. That really signals the guy how important the date with him is, he's got top priority.