USCF Official Rules of Chess, p.86, Para. 20D, Use of Additional Chessboard or computer prohibited. "A player who analyzes a game in progress on another chess board or consults a computer about the position is guilty of a serious violation of the rules. Though the director still has discretion, the usual penalty is loss of the game."
20N. Electronic communication devices. "Players are not allowed to leave the playing venue without permission from the arbiter. The playing venue is defined as the playing area, rest rooms, refreshment and smoking area, adjacent hallways and other place as designated by the TD... " Without the permission of the TD a player is forbidden to have a mobile phone or other electronic means of communication in the playing venue, unless they are completely switched off." Violation of these rules could result in loss of game or even expulsion from USCF competition (if the case is severe - major prize money events).  - NMLF STD