First off, is the phone unlocked? (meaning that you are free to use the phone on any carrier
Your phone needs to be unlocked when you switch.
Second, since your device is an iPhone 6 you can use it with just about every carrier. The iPhone 6 models and newer can read both GSM(AT&T/T-Mobile) and CDMA(Verizon/Sprint) technology.
We have created a search results page of available plans with your minutes/message preferences. These plans won't cost much due to them being strictly texting and calling. Since your phone is versatile with just about every carrier, you can explore all BYO options.
You can click here to Compare All BYO Plans
During the sign-up process, you will have an option where you provide a number you would like to bring with your phone or an option to get a new number. Once you find a carrier, contact them after signing up for the plan and activate a phone number.
If you find a carrier you are interested in, but there is no direct purchasing link supplied, you will need to go to that carrier's website in order to buy that plan.