i don't use it, but i know it does use data. i'm not sure if it uses any more data than any other messaging app though? it's an "instant messaging" app (as opposed to text messaging), which means it stays running/open and the text is sent and received instantly, over the data network. i use AIM (aol instant messaging) at work with coworkers, and gtalk (google's instant messaging service) on my phone. it's a great way to communicate.
Thanks everyone! So far I like KIK and doesn't seem to use a lot of data. I don't send pics and such which I know uses more. I don't have text on my phone, can't afford any higher monthly bill, This will work good for my daughters, in Kentucky , Texas and Arizona.
you should look into "google voice." i believe you can send actual texts with it, without them being "texts" from your phone. you can do a TON of other stuff with it as well......all through your data package i believe.