You can have a cell phone in your pocket but they won't let you use it for anything. I suspect in the era of smartphones that they would completely ban them from the floor if not for the fact that enforcing that rule would be a nightmare.

Source: I've absent mindedly taken a call while sitting down at a table in Las Vegas and got an instant warning from the dealer.

No cell phones allowed at the tables. If you want to use your phone you have to stand up and walk away.