If I send a group text, will my contacts be charged for those by their carrier?

Most wireless customers have unlimited data plans, but it would depend on the customers service plan. When you send out your first text, the contact numbers must opt-in by typing OK or CPC to see your message. They only have to opt-in once. They will start receiving your text messages. They can opt-out at any time by typing STOP. You just want to make sure they are text-able numbers.