I have the same request. The idea is that the RUTxxx checks the POP mailbox and pulls down all the emails. It then looks for the phone number in the To: field, xxxxxxxxx@sms.example.com. as mentioned. There would also some sort of basic security such as "Only forward emails from this domain".
On the email server side, sms.example.com is set to a catch all, so anything at that domain goes into a single mailbox.
The specific workflow is that you can then put these special email addresses into a users address book. They can create a new email and send it to John, Greg, and Sharon. The body of the email becomes the SMS. The email gets sent, and the RUT pulls down 3 emails, each of which gets sent automatically. It makes automation very easy.
You also wouldn't need to precede the number with 00 or anything like that. It would just be <number>@sms.example.com. Very easy for staff to understand and send SMS's.