the address for sending sms to a phone with at&t is, firstname.lastname@example.org
If you have a WAP enabled phone the address for sending MMS is similar
When sending text messages from an email account send it in PLAIN TEXT format. Rich text format could be multiple pages even for a short message and result in a charge for reading each page. You can set it in your email clients address book to always send plain text format to that email address.