Chosen Solution

Where it is saved in the iPHone IMEI?

Settings>general>about

You can’t, period. Apple is a group of control freaks, they paired and encrypted almost every chip that has logic functions. So replacing just some of the chips will destroy the device. For example in order to replace IMEI, the baseband and baseband flash ROM chip must be replaced together as a set, or the device dies. Also the device S/N must be rewritten to pair with the IMEI, or the phone will be denied activation. Rewriting S/N is not yet possible for iPhone 6s, so just forget about replacing chips. If you replace the logic board, you’ll run into another problem. The Touch ID sensor is paired with the CPU, Touch ID dies immediately when you replace just the board, and if you attempt to reinstall iOS, jackpot, the phone dies.

Baseband chip is the one with the IMEI.

imei saved in iphone on eeprom ic