You don't have a "right" to be on private property (restaurant). Get up, get a doggy bag, walk out.
Neither of us (you or me) know whether or not it was a safety measure. If the Secret Service says "yes", then it may be "yes".
Is it inconvenient if you are there having dinner? Yes, but guess what? Your plane will be delayed when Air Force One lands and takes off, and you'll sit in traffic if the President is in the area. Neither are "unconstitutional".
These people didn't lose their phones. They lost temporary access to them because the Secret Service thinks it's a good idea.
Kennedy, Reagan, McKinley, Lincoln and Garfield were shot. A man tried to kill Kennedy with a dynamite rigged car. Presidents Ford, Franklin Roosevelt and Truman were shot at. A man attempted to hijack a plane to assassinate Nixon. Someone tried to hit the White House with a plane to harm Clinton. Someone else fired at the White House to harm Clinton. President Bush has a grenade thrown at him. I'm sure that's not a complete list. It's just the ones I can recall off the top of my head.
All this leads me to think that if the Secret Service thinks cell phones are a problem on private property (which a restaurant is). I'm taking their word that they know what they're doing. Don't like it? Walk out.
Sorry dude. Not buying it. This was an ego trip for Obama. Nothing more.