These settings are found at:
Configuration -> System Setup -> SMS
SMS Sender Number
When left blank, the SMS will show as being from SwimSchool.
You can change this if you wish. This can only be 10 characters in length (the length of a phone number), including spaces. It must only be made up of letters, it cannot contain any numbers. DO NOT enter a mobile phone number in this section or your SMS messages will not send.*
*In order to send SMSs through your system, you must have an activated SMS account for your site. If you do not have an SMS account, you will not be able to send SMS messages through your site.
If you would like to activate an SMS account, please contact Support.