Being new to the whole mobile phone world, I have to ask: Do most IM programs send their IMs over the data connection, or as SMS messages? I'd love to be able to stay in contact with my IM friends on-the-go, but I don't have any kind of SMS plan, and don't plan on ever paying for that overpriced mess. I installed the Trillian beta to my new Desire, but haven't used it yet, I'd like to be very clear on whether or not I would be receiving a bunch of text messaging charges at the end of the month.

Trillian uses your data connection to send and receive messeges and also to check for online availability of your contacts.

* disclaimer - I do not work for Cerulean Studios or RIM *
* I am only a long time Trillian user who loves his BlackBerry *