The other guy is 100% except the last part about the limits. While it theoretically COULD put you over the limit. The average text message even with video would be lucky to average a couple of megs per conversation using a cam. Otherwise, it would take all day to get 1 meg of usage. Most ISPs offer several 1000 megs of usage. I doubt you would go over for chatting...
If you were referring to Skype or one of the similar services using actual voice, then yea, but it warns you up front about the costs, no hidden fees. If you're implying instant messaging...again, like the other guy said, its free.
