T mobile internet plans?

Ok well im planning on getting "the dash" phone from t mobile. I was looking at the internet plans for it and i can see that its 30$ to unlimted internet and data with 300 text messages, well the phone i want has AIM on it and i was just wondering if anyone knew that if you are on AIM and sending ims and reciving IMS does that count as text messages or just sending data??? if it means text messages then i think im just going to get a sidekick 3..how is that phone by the way?