There should be scheduled times for SMS messages, and also a maximum number of SMSes in a period. For example, our e-mail queue stopped overnight and when I woke up in the morning I had lots of SMSes on my phone, and it used up our monthly allocation. I have added my own setting to define the times when SMS alerts should be sent, so they are not sent overnight while I'm sleeping. But being able to set a limit of e.g. 10 SMS alerts per hour should also prevent too many being sent.