I think this is not really an issue anymore since we've started to urge people to pay until they do.
Also, only 10% of the students [as of 3rd of July 2018] are non-students. I think it's not worth the effort of searching an SMS provider with a nice API, a library compatible with it etc. We should instead focus on the students by implementing Shibboleth and live with the fact that there will always be one or two people that won't pay.
I think this is not really an issue anymore since we've started to urge people to pay until they do. Also, only 10% of the students [as of 3rd of July 2018] are non-students. I think it's not worth the effort of searching an SMS provider with a nice API, a library compatible with it etc. We should instead focus on the students by implementing Shibboleth and live with the fact that there will always be one or two people that won't pay.