SMS, or Small Message Service, only allows you short text messages, no file transfer and no smilies. That is as close to an IM client as you can get, without a BIS and data plan.
ok, thanks for the help. i'm just kind of disappointed because my previous phone which was not nearly as good as a blackberry could use SMS based IM's. And i can't switch plans because for t-mobile the data plan is twice as much as the text.
More than 1 of my friends has a smartphone without a data plan. But I don't get it. I think it's like having a wife without the "love" (take that however you will)
With texting you can text whoever you want. OBVIOUSLY. But with a data plan you can BBM/MSN IM/Gchat/AOL IM/ Yahoo IM/accessing ANY website / everything else. Depending on who you are talking to maybe a data plan will work best. Maybe a texting plan will work best.