I have an AT & T Samsung with the following problem:

Under the Mobile Networks menu, the phone does not allow the selection 2g, 3g, 4g/LTE etc . Instead it just allows Mobile data and enhancedLTE services to be ticked

If I look further ...under Device Info, it has the following options: WCDMA preferred, GSM only, WCDMA only,,CDMA only, CDMA auto Ev/Do only, GSM/CDMA, LTE/CDMA,LTE/GSM, LTE/GSM/CDMA, LTE only

After many trials, I found that none of these settings enables the phone to automatically select the best radio channel for either calls or the internet...except that the phone does its best to hang onto GPRS and some 4g signals only when set to WCDMA preferred

Any of the other settings if selected , even if it the phone shows a strong signal connection,( eg. 4G) .....network calls made to the phone simply don't connect....and there is no no ringing indication.

I am unfamilar with the impact of APN settings..but is it possible that even though the phone is unlocked, that some other settings might enable it to operate happily on Vodafone NZ's great network? Or am I in a dark space with this phone?