The short answer
Verify unlock status, network compatibility, eSIM support, and number-transfer details before moving an existing phone.
Step by step
Find the phone's exact model number and IMEI in Settings; a product family name alone is not specific enough.
Confirm with the current carrier that the device is paid off and unlocked, then verify the status in the phone settings when possible.
Run the destination carrier's IMEI compatibility checker and confirm support for the network and features you need.
Back up the phone, save account credentials, and obtain the old carrier's account number and current transfer PIN.
Activate the new SIM or eSIM and test calls, texts, cellular data, voicemail, hotspot, and emergency-address settings before closing the old account.
Before you finish
Keep screenshots, receipts, chat transcripts, confirmation numbers, and the first bill after a change. Carrier terms and account eligibility can change, so verify the final price and conditions directly before submitting an order.