how to check imei to work on network without calling att
I need to buy a phone used. I want to buy it once and be done. what website do i put in the imei to find the exact model number as deemed by att. for example the samsung a51 has some numbers after it on the list provided by att but when you get a phone with the exact same numbers and try to activate it the att rep says that it has some more numbers not visible to the customer. I want to find that first. HOW!