...
Depending on your settings, you might have the system send an SMS to staff rostered tentatively as a way to reduce the time required for staff to confirm they're able to assist for a shift. These messages will come from a random set of phone numbers, in order for us to then receive responses your staff have sent, and match those up to the relevant event they're referring to.
Where replies are expected, other numbers such as your company name, or a central company number can't be used as the system won't receive these responses (your company phone number will get sent these!)