What does the letter 'D' mean in iPhone's serial number?

Apple has been transitioning from logical serial numbers with meaning, to more randomized serial numbers without meaning. So the structure of the serial number won’t help you with recent devices.

You can check the status of a device by serial number, which would tell you if it corresponds with the actual device model that you would expect. Check your service and support coverage - Apple Support

You would find genuine Apple products at Apple Authorized Resellers and Apple Stores. Those would not be fake, and wouldn’t have counterfeit parts.

If the iPhone runs iOS (duh), then the the iPhone itself would be able to check for any hardware changes: About iPhone parts and service history - Apple Support

Is this a fake?

The only letters of significance are in the MODEL number, not the serial number.

We bought our iPhones diectly from a major carrier and their model number show the "new: code M, and we had no issues adding them to our Apple accounts. Both serial numbers start with "D."

Best way to check for "genuine" is to enter your serial number into this Apple support page:

Check Your Service and Support Coverage - Apple Support

The letter codes for the MODEL number are as follows:

— If the model number starts with M, it was purchased new from Apple or a major carrier.

— If the model number starts with F, it was refurbished by Apple or a carrier.

— If the model number starts with P, it was sold as a personalized device with Apple engraving.

— If the model number starts with N, Apple provided it as a replacement device for a device returned for service.   

Again, these DO NOT apply to serial number letter prefixes.

Apple has used randomized serial numbers for a while now where there is no meaning with any of the starting letters. It used to be that you could figure out where it was manufactured using the serial number, but that is no longer the case.

Your Model number may be used to provide some information based on the first letter:

M – Brand new device, meaning the device was purchased new

F – Refurbished device, meaning the device has been through Apple’s refurbishing process

N – Replacement device, meaning the originally bought device was replaced by this model likely due to a service request

P – Personalized device with engraving, meaning the device was customized with an engraving on purchase

The serial number can consist of any random mix of letters and numbers. The are no "codes" to tell you anything about the phone.

The Model Number is more useful as providing information about the phone. Your Model Number should start with an "M".

Do you live in Germany?

My Model number start wıth ‘D’ (

It doesn't. That's a serial number.