A Garden Without Walls – SMS on XMPP (Jabber)
"XMPP is the open standard for messaging and presence." (https://xmpp.org). It is also known as Jabber.
While some companies (Google, Facebook) have (ab)used this free standard to make their own Walled Gardens, there is another group that is using it to move technology forward: JMP (https://jmp.chat)
JMP allows you to get a real phone number and use it for texting, calling, group texts, picture messages, and yes - it can even receive messages from short codes. You can use it with any XMPP-capable client on any device with an internet connection. You can also use it with a SIP client to make and receive VoIP calls.
Unlike Google Voice, JMP does not mine or sell your data. Also, you can use/buy JMP's service completely anonymously. What is the "backend'for this? I mean do they use something like twilio or something else? I am asking cause I think most such services use SIP instead of xmpp, although for messages xmpp might fit better. The backend is Bandwidth. Since JMP uses an actual carrier instead of a reseller like Twilio, it is easier to fix issues and get questions answered, as there is one less level of tech support indirection. It also means JMP's costs are lower (Twilio is extremely expensive) and gets more features (Twilio doesn't do group texting or messages to short codes). While SIP does support messaging, it is extremely limited: text-only and single recipient (no picture messaging or group texts). So XMPP is a much better fit, as all the texting features people expect can be implemented over XMPP.