Does it cost money to text a iPhone in New Zealand?

My Bff and I both have iPhones and she moved to NZ and got a NZ number. I live in Hawaii. Can we Imessage for

You have to call your cellular provider to ask about costs. Same for her.

You most likely going to have a charge even if both phones are NZ numbers. It would be easier to Email, Facebook or Skype.

Internationally there's always a cost, there are better and cheaper ways, as already pointed out, Skype or email work well