Twilio

 Twilio  is an SMS and voice telephony service. You can set up Twilio to make and receive calls over HTTP, and more interestingly to send and receive SMS as well

Features
This section is a stub, please expand!
 * SMS API
 * POTS API

Implementations
tommorris.org has had Twilio-based SMS integration since 2013-07-13:
 * I can send an SMS text message to a UK-based landline number from any phone and the content of the SMS gets sent via HTTP POST webhooks to a private endpoint on my site. The body of the HTTP POST message contains XML that lists the phone number it came from, the content of the message and assorted metadata. If it came from an authorised number, it is posted to my site in the same way that a post submitted on the web would be.
 * After the post has been made, my server sends back a blob of XML to the server in the response, and Twilio sends an SMS message back to the phone with the URL of the post. The post is tagged as being "via sms" (in the old style of Twitter)—examples:.




 * I went to France earlier in 2014 and had no roaming on my iPhone. I wanted to post something to my site, so I could actually post it from my £10 Nokia 1000 pay-as-you-go phone while roaming in France.

wrote a piecemeal Google Voice clone using Twilio, called Bagel Voice. It's pretty shoddy and needs rewriting, and the Twilio service offerings have also expanded since then.

Ideas

 * checkin!