Well, depending on the carrier/service provider, that device may not have a SIM. Not all of them do. So you would need to check with the company you got the phone through.
the IMEI number can also be called the MEID number on some devices. This should be in the "Settings" then "About Phone". You may have to tap another area in the "About Phone" section, deepening on how it is set up in the Android version you have. The info should also be behind the battery.
You can all try typing *#06# into the phone dialer.