Can I spy on my employees if they use my company supplied cell phones?

I believe i have a thief in my company and need to know if one of my sales guys are stealing from the company they all use company supplied cell phones so would it be illegal to see what they are doing by watching there calls, text, and emails etc...?

Legally speaking yes, if you provided the cell phones and they are for business use only then you as an owner have the right to watch what they are doing.

I saw a story on the news last week about an owner tracking a sales guy that was stealing and funneling money from the company, this idiot used the company phone to do all his dirt and the owner used this little app on all his cell phones to track the guys phone calls, text messages etc and they caught him with all the evidence they needed....the app was called mspy i think and their link to get the app is here: bit.ly/TaYULV