https://en.wikipedia.org/wiki/Webhook
To me it just seems obvious that there should be an either/or option for SMS or HTTP especially since a metric shitton of people are already using slack and hipchat.
The transmission costs for HTTP are way more cheap than SMS so it seems like it would be in you guy's interest to support webhooks in order to reduce outbound SMS costs.
TLDR; HTTP is the new SMS
If they did do webhooks then you could write one that sent out SMSs though - leave them to do the hard part while cutting them out of the loop!
Also I think it's push notifications, not SMS.
Really it's up to the startup.. do they want to try to eventually become the Internet's primary notification propagation channel or are the only interested in catering to a particular mobile phone use case ?
Actually we are working on adding Hooks as an IFTTT channel later this month as a trigger so anyone can build their own receipts.
However, now that IFTTT supports push notifications, why do you still need Pushover or Pushbullet?
[2] is my crappy push notification service mostly built for my own usage because PushBullet started getting more bloated and annoying.
[0]: https://developers.google.com/web/updates/2015/03/push-notif...
[1]: https://developer.mozilla.org/en-US/docs/Web/API/Push_API
We are also working on notifications API for Chrome as the next step for the web interface.