We provide subscription management using CB Paid Subscriptions.

www.joomlapolis.com/addons/cb-paid-subscriptions

What specifically are you wanting to integrate? If it's simply to send data to an external system that's quite easy to do with core CBSubs and its CBSubs URL integration that lets you send an HTTP request to an external system including subscription data. For more advanced cases you'd likely need CB Auto Actions as well though.

You can use Joomla 4's task scheduler or CRON to run auto actions on whatever schedule you want. We don't have any functionality for sending SMS messages so you'll need to implement that yourself, but yes that's doable using CB Auto Actions assuming you've the PHP experience to code that. As for included with CBSubs we only support sending emails or on-site private messages on schedules.