In some industries the ubiquitous cell-phone camera is a liability. I have friends and family with security clearances who are only allowed to bring phones without cameras into work. Finding such a phone these days is actually kind of a pain, enough so that several of these folks just don't have a cell phone.

I have a security clearance and have worked in the DefCon industry for about 3 years. Every secure room area I've had has had an area for you to lock up electronic devices you might use outside of a secure area, such as cameras, flash drives, and cell phones.

Other contractors I know in the west coast just leave their cell phone in their car when they go on base. It just sounds like your friends are using the old "I have a security clearance" excuse to not have a cell phone, which, if its the case, more power to them. :)