to my knowledge, this cannot happen without someone actually locking the sim, so you may want to contact your employer, but just in case your employer doesn't know whats happening,
here are instructions to find your puk code for att, if you have a different carrier, contact their customer support for further instruction
Obtain a PUK Code
When the error message "ENTER PUK CODE" is shown on the screen of the device:
- Log into myAT&T.
- Select Wireless from the myAT&T tab at the top of the page.
- Select Phone/Device.
- Click Unblock SIM Card.
- A new page will open, containing the PUK code for your phone. Enter the code on your phone's screen to unblock the SIM and create a new PIN.
Unblock SIM Card
- Enter the eight-digit PUK code on the phone, then press OK/Yes.
Note: Some Motorola phone users need to enter **05* if "enter PUK" is not already displayed. After entering **05*, enter the eight-digit PUK code and press OK.
- Select a new PIN code, then press OK/Yes.
- Re-enter the PIN code, then press OK/Yes.
- If the codes were entered successfully, the phone is ready for use.
If the incorrect PUK code is entered 10 times in a row, the SIM card becomes permanently locked and a new SIM card must be purchased. If the device is requesting PUK2, call Customer Care at 800-331-0500.
... good luck