I know this, i already told him about CDMA. That's why CDMA devices should be avoided to begin with. There is no permanent solution to this issue, especially on some older CDMA devices. The carrier based phone firmwares and modem (hardware) are optimised to run on that specific GSM or CDMA carrier.
Bootloaders can be unlocked, so no big deal, but CDMA is the deal breaker.
CDMA and GSM are two different things, even on hardware level, so software modifications doesn't help much. But the CDMA phones have some compatibility (though limited) with GSM, this is why they can be GSM sim unlocked. After unlocking, they search for both, but the priority is CDMA over GSM, like you said. Service mode can reverses that priority too. In some phones, this tinkering may help sometimes, though not all the time.
There is no harm in trying this simple code as try. It won't brick the device [emoji4].
That error notification can be vanished usually by removing Verizon bloat by rooting.
True about band frequencies. No doubt S3 CDMA has more complaints on GSM, though many CDMA phones run satisfactorily on GSM.
