I am using 2degrees SIM on my Samsung I8262 Galaxy Core Duos (got from overseas) mobile. But, unfortunately, sometimes I am unable to make any phone calls or use mobile data as is keep saying "Not Registered on Network". However, is works fine some times.
Can you please help me if I have to do any settings in the mobile.
Please double check your settings are correct - http://www.2degreesmobile.co.nz/settings - making sure 'Network mode' is on Auto (GSM/WCDMA) and not WCDMA or GSM only and Network Selection is on Automatic too.
Try a manual search if it's not connecting in future to see what networks are showing.
If it's still an issue try the SIM in another device and take it to a 2degrees, Harvey Normans, Dick Smith or Warehouse Stationery if it's still happening and they can try a SIM swap.
Here's more info - http://www.2degreesmobile.co.nz/help/simcards.