Does it cost any additional money to "Forward IMs" to a Cingular phone, with text messaging already enabled.

I have a Motorola V3 Razr (I don't know if that's significant or not). But I found a thing on AIM.com that allows you to forward IMs to your cell phone. When I sign off of the Computer's AIM, a little phone icon will appear next to my screen name [on someone else's buddy list]. And when someone does IM me, I receive the message as a text. Does anyone know if this text I receive costs any additional money. I have the 1000 text plan with Cingular. Does this use those texts, or does it cost extra?