The Nokia 6500 slide is a tri-band phone that was released in 2007. If you purchased this phone with a contract, it may have come locked.
This means that you will only be able to use it with the network that you purchased it from. If you would like to use another service provider you will need to unlock the phone. This means you will need to retrieve your international mobile equipment identification number (IMEI), which is necessary to create an unlock code.
Turn your Nokia 6300 on. Type in “*#06#” Wait for the IMEI to appear. This is a 15-digit code. Once it appears write it down. Open the case and remove the battery if you were unable to find the IMEI by dialing. Look for the IMEI underneath the battery. It will be typed out on a sticker.