So you are saying that a phone will drop down from umts or lte to gsm if the gsm signal is the strongest? i know it will resort to gsm as a backup, but i though

So you are saying that a phone will drop down from umts or lte to gsm if the gsm signal is the strongest? i know it will resort to gsm as a backup, but i thought this happened only if 3g/4g was altogether unavailable?