Using illegal software downloaded for free to unlock CDMA mobile phones is unwise and probably unnecessary since many carriers accommodate unlock requests, and newer CDMA phones are not locked. Using free software invalidates any applicable warranty coverage, exposes the phone to malware and risks making the phone inoperable.
Most carriers accommodate requests to unlock CDMA phones, especially when there is no contract obligation remaining from a discount given at the time of purchase. CDMA providers are aware of the limitations of using CDMA phones abroad and normally agree to such requests. It is definitely worth asking rather than unnecessarily risk damaging the phone and the relationship with the provider.
Verizon Wireless, the nation's largest CDMA service provider, claims that is newer 4G LTE phones are GSM-ready and are already unlocked as of January 2016. They do not need codes or software for activation on GSM networks.