I was at work and set it up this afternoon. Left work. Drove home, connected to my home wifi. Made some dinner then got a call on my home phone from mum to say she tried to ring on my mobile.
Sure enough toggled flight mode on then off and two missed calls notifications and a txtmessage came through
Of interest is a message on the notification shade which I haven't seen before "SIM not allowed for voice" and the same "Emergency calls only" where it usually says Vodafone NZ
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As previously stated, this would seem unrelated to the issue this thread is about, and appears to quite likely be a signal strength issue. You previously mentioned you were rural.
To find the signal strength on the Galaxy you would go to Settings, About Phone, Status, SIM Card Status. The signal strength will show as a number like -70dBm 60 asu
The less negative the dBm number is the better the signal. The higher the ASU the better
Not sure how you get similar details on the OPPO.
As a rough guide
-50 to -79 dBm, then it's generally considered great signal (4 to 5 bars). -80 to -89 dBm, then it's generally considered good signal (3 to 4 bars). -90 to -99 dBm, then it's generally considered average signal (2 to 3 bars). -100 to -109 dBm, then it's generally considered poor signal (1 to 2 bars).
Yes -108 is getting pretty low. Remember dBm is a logarithmic scale. For each 3dBm decrease you are roughly halving the signal strength.
I cannot be certain that could be the cause of your issues. Your only real option may be to nag your service provider or go stand on your roof.
@Montana308 -108 is not to bad for 4G but not the best for 3G
Just remember if you are doing nothing on the handset then this is just camping on a cell and as soon as you do something it might hand to another stronger band
So handset could be camped on 1800Mhz 4G -108 and then can quickly change to 700Mhz 4G (Guess -85 or -90)
Open the field tester on your handset and you can see how fast it changes between bands when required