As mentioned earlier, many CIOs aren't on the wireless management ball. These companies spend an average $80-per-month for a company-owned smartphone, or $10 more than a BYOD smartphone. At first glance, this seems to prove BYOD's cost savings, right? Wrong.

You'll have to tack on the hidden cost of reimbursing BYOD employees. Typically, an employee files a monthly expense report for their wireless bill. A single expense report costs about $18 to process, says Aberdeen. Suddenly, the cost of a BYOD smartphone bill runs around $90 per month.

It should be noted that an employee who files an expense report with multiple expenses, including the wireless bill, will still only cost the company $18 to process. That is, mobile BYOD expense reporting will incur this hidden cost only if the expense report was filed solely because of the wireless bill.

BYOD employees often expense their entire wireless bill rather than itemize it. "There's absolutely no visibility into what's personal and what's corporate," Park says. "Even though companies may say they take care of this by putting in a ceiling or fixed expense amount, it doesn't mean they've optimized the cost structure. It just means employees know how high they can go."