Having worked with two variations of SMS Delivery, I think we could simplify SMS setup for the staff/patron.  Instead of just filling in a phone number, what if the SMS number gave the following options: 1) Use the primary number 2) Use the secondary number 3) Provide a unique number.  The third option could reveal a new text box to put a number in.  Honestly though, I think we could get by with just using the primary or secondary number fields.

I also think that in the SMS setup, you could select from popular services, and have Koha format the number as needed.  If using e-mail, it strips out all non-numbers and checks that the number is the correct length.  If Twilio, it makes sure number is stripped of non-numbers and +1 or whatever is added to the beginning.  Since different countries have different formats, and phone numbers can be entered in various ways, maybe we could have a custom regex entered to reformat according to your specific uses.

The approach that we currently use here is that we have an example format in the SMS number field, and I created an icon to copy the primary phone number, stripping non-numbers and adding a +1 to the beginning.  I added another icon to clear the field.  It has improved the process vastly.