Take care,
SMS is slow. .. if you send many alarms via SMS you have to queue them.
On linux there are several services available to do this job. Sometimes they use multiple Mobile-phones or UMTS-Sticks to provide a fast deployment of mass-alarms-SMS.
There are a couble projects running on rasberrypie to queue the SMS-Alarms. .. but only with one UMTS-Stick.
A simple solution could be to create only a File for every alarm and then build a scheduled job which only grabs all files every 1 or 2 minutes.
Finally only this job and the files create a simple queue.
.. if there are to many files, kick only one alarm-sms "too many alrms to send them induvidually"
If you use an external service, ... what is the plan if this exernal service fails? *-)
Regards
Erich