Yahoo does allows hutch but you can try and see for thers .Yahoo at present is Free while msn charges the receiver of the message I think double the amount that is normally charged.If the person replies to that message he is charged
chk this out for further details Yahoo SMS
If you are using yahoo mesenger then simply follow these steps...
1) login to your account
2) click on the icon written "TEXT" with an icon of mobile
3) write the phone number in this format +91-98-------
4) write ur message not more than 144 characters
5) click on send