Small update for anyone interested in using this.
It's working very well in my trials.
I have it sending an SMS to the user when each ticket is created. It basically informs them that a new ticket has been created and to check their registered emails for further updates. Which is perfect as I don't think most people would want SMS sent to their phone for every ticket update, especially as responses can be detailed and require attachments.
The fact you can include ticket/user/organisation data within the SMS is really great. I have it showing the ticket ID and organisation, so the receiver knows exactly what it relates to. You can even have a link to the ticket thread in the SMS, but I have removed this as I think less is more in this case.
Looking forward to going live with it.