AIM along with Blackberry Messenger (PIN) uses the data network. As long as you have an unlimited data plan, then it won't cost you anything to use it other than your monthly data fee. The messages are counted towards data usage and not text messages. Along with StreetDocRn, I would suggest to monitor your usage by logging into My Verizon. Also you can check your usage by dialing #DATA from your Verizon Wireless device.