How to back up your IMEI
This is the most important things to do before flashing any rom or apps is to backup your imei.
After flashing ROMs or installing updates, it is possible that the phone will get an invalid IMEI or unknown baseband. Invalid IMEI would mean no mobile network connections.
Every mobile phone, GSM modem or device with a built-in phone / modem has a unique 15 digit IMEI number. I have 4 methods to back up your IMEI.
Set your phone in USB debugging mode, then connect via USB cable.
Open mtkdroid tools
Nowadays there’s update in some custom recovery like twrp, philztouch and ctr that has nvram backup and restore menu. You can backup this nvram/imei by means of this custom recovery.
to the developer of this tools