I commonly work in a clean-room (CR.)
Huge signs in the grey room saying "NO CELL PHONES"... ahhh... but everyone's cell phone was special!
And how does the claim "my cell phone is special" wash when the security guard is patting you down to check for contraband before you enter the work area? You know, the security guard who has had it explained to him - in writing, above his fresh signature - that if ANYONE in the are that he controls is found with a cellphone (or other contraband), then he gets fired. The guy who works for a different (outsourced) company, works a different shift pattern to you, and will be rotated to a different site (for his company) at unpredictable intervals. Work patterns designed so he (or she - you'll need female guards to pat-down the female staff) never builds any sort of relationship with people at your company, because his (her) job is to enforce rules, not be nice to people.
Frankly, if your company is losing valuable product and equipment to such contraband, then they have no real option but to implement such rules. And it's not uncommon. When I take my helicopter to work, I get the pat down - everyone does, and has done since at least the mid-1970s. When my wife goes into her office, she's required to have her bag searched for telephones (not allowed) cameras (of any sort ; not allowed) and memory devices (of any sort, including MP3 players ; not allowed) between reception and her office. Lockers are provided - "put your stuff in there and take the key", and then they're searched.
Neither of us work in classified areas - they're banned on our helicopters because there have been incidents of transmissions scrambling navigation equipment (30 years old ; no reason to upgrade) and there have been people miss important announcements ("we're diverted to platform X first, not Y ; don't get off at the wrong stop") because they were listening to a Walkman. Diverting a flight to pick up a lost person costs around £5000. Music players are forbidden while flying (and they interfere with the hearing protection anyway). My wife sometimes works with medical records and other times with financials. So the office operates on information security. Senior personnel who may need to be contacted when not at their desk carry DECT-like phones that connect their desk to their pocket - with no data storage apart form an address-book, manually entered.
What is your business case for needing your phone in the RF-free area?