There are options, but none through iChat. First,
GizmoSMS allows to send SMS to quite a few countries for free. Some people on their forums have complained about messages not being delivered, but I haven't used it myself as it doesn't cover countries I'm interested in. I trust that company in general and use their Gizmo Project software as an alternative to Skype.
What I do use and like is the
smsmac widget. I like it for two important reasons (for me): (1) I can get replies to my email, so I don't pay for incoming messages (does not apply to US recipients - bummer), (2) integration with Address Book contacts, so I don't accidentally mistype a number.
Another way I'm hoping will be improving is through
callwave. The problem with them is the Dashboard widget doesn't work for me under Leopard, and while they
mentioned on their blog last month about adding the reply to email option, they've been quiet about it since.
There's also
sendsmsnow with some free countries to text to. I have no experience with that.
