How do i unlock my verizon zte and my straight talk lg codes?apn? Please

Hi my son and I will be going on a trip soon and I need help to unlock our phones so that I can use our att prepayed. Sim card to stay in contact wile we travel. We have a straight talk prepayed LG and a zte. From Verizon I have contacted both companies and no help so I have looked online tried many apps and don't have a credit card or the spare cash for a unlocking company I am not sure were to or how to find the unlock codes can I justcchange the apns or what do i do can someone please tell me how to unlock my phones were do I find the apns and or codes any guidance will be greatly appreciate