For SMS, we depend on the feature that (AFAIK most/all providers support?) sending an email to a particular address would trigger an SMS message -- e.g. see http://www.tech-recipes.com/rx/939/sms_email_cingular_nextel_sprint_tmobile_verizon_virgin/
... so the email notifications feature in Jopr should satisfy the requirement to support the need to send SMS messages.
Mazz is correct. The larger question at hand is whether we have a mechanism where users can implement there own custom notification schemes today, and that answer is no. It has, however, been discussed in the past, so don't be surprised if you see it in a future version of Jopr. : )