No electronics, including cell phones, can be used while seated at a casino game. The thick walls of most large casinos block cell phone reception anyhow so you have to walk outside to get a dial tone. In the sports book of the casino, pagers and cell phones cannot be used at all.
Shouldn't be a problem while playing slots. At tables you may be expected and/or asked to move away from the table to make or receive a call. An absolute no no in and around sports books. Making or recieving a quick phone call on the solts is no problem.