Need help with Aim application for w580

I recently flashed my w580 form AT&T. It originally came with an aim application. It would send messages as SMS(or something like that, in other words it was free). I know there are messenger apps that can do the same except that they all have to use internet and as such will charge me for usage. I have unlimited texting but not data usage. Does anyone know where I can find a messenger(aim) app that would send messages as sms without using any data? Thanks.