I have an iPhone 15 Pro Max with 2 IMEI numbers

iPhone 15 Pro would have two IMEI numbers because the phone is a dual SIM phone. Just like iPhone 16 Pro would have two IMEI numbers. I once had to have AT&T correct the IMEI number in their system for one of my iPhone's, but don't remember exactly which model. When you say you are trying to get the phones to sync, exactly what are you trying to do? Transfer the data from the 15 Pro to the 16 Pro? Please provide more details.

Even if your device uses an eSIM and has an EID (Embedded Identity Document—a unique identifier for the eSIM chip), it will still have two IMEI (International Mobile Equipment Identity) numbers. This is because modern smartphones, particularly iPhones and many Android flagships, support dual SIM functionality, allowing you to activate and use two SIMs simultaneously—whether they’re both eSIMs, or one physical SIM and one eSIM.

While one EID can support up to 8 different eSIM profiles stored on the device (for example, when traveling internationally or switching carriers), you can only activate two SIMs at the same time—one corresponding to each IMEI number. Each active SIM must be tied to a separate IMEI, which allows networks to recognize and manage them individually.

Importantly, IMEI numbers are hard-coded into the device at the hardware level and do not change unless the device is tampered with. Any attempt to alter or spoof an IMEI number is illegal in most countries, as it’s considered a violation of telecom regulations and often associated with fraudulent activity.

So in summary:

• One EID = up to 8 stored eSIMs.
• Two IMEIs = only two eSIMs (or SIMs) can be active at a time.
• IMEI numbers are permanent and tampering with them is against the law.

when we switched over to AT&T I noticed I have two IMEI numbers.

The iPhone 15 would have two IMEI numbers no matter what carrier you might have used or will use in the future.

When I try and have a repair through our warranty, they say AT&T is showing incorrect IMEI #.

Who is "they"?