What is effected by Changing logic board

I replaced iphone 6 logic board and home button with used parts (from a smashed phone I verified had been paid in full). When I trurned on the phone at first it showed lifetime call time of 2-3 days. After inserting my sim card it showed lifetime call time 0. Is this normal? Does replacing the logic board change anything else (other than imei). I was able to complete icloud activation but after brief searching and momentary connection showed no service although wifi calling was active. I talked to tmobile, at first they said phone not in system, then they said it seemed to be associated with another account possibly cancelled, not reported lost or stolen, and no money owed. They are supposed to research and get back with me, but I'm wondering if changing the logic board can cause changes that i should be aware of.

I apologize this is so drawn out.