Those are IMEI label examples of the different phone models. You can recognize IMEI by 15 digits (without other characters like slash “/” or minus “-” or spaces etc…)
Nokia 6020 label
Nokia 6020 IMEI label
Samsung SGH-L700 label
Samsung L700 IMEI label
Nokia 3100 label
Nokia 3100 IMEI label
Nokia E51 label
Nokia E51 IMEI label
Do you know if QR code on Nokia IMEI lables are standard QR code format or bespoke to Nokia?
Just tried with my Nokia E71 QR code under the battery (on the phones back) and scanned QR code with Android application for QR codes and it read IMEI and CODE
35271004009xxxx;0561xxx