[Gogar]

She can use iChat and it will go right to any mobile phone. In the iChat window for each person, you just have to enter their mobile phone #. If they are not "online" as a buddy, anything she types will go straight to the phone, any reply they type will go right to her iChat.

You don't need any extra anything.

If you or your family doesn't have AIM screennames, you can always go to iChat and use

File -> Send SMS

and type in a phone number and send a text to it.