Hanging out on the floor at Twiliocon, Josh - you should come!
Great questions - as you can imagine there's not a whole lot I can share about the relationships with our carrier partners. Working with them was essential to bringing this product to market, and we sincerely appreciate all the hours they put with us on getting Picture Messaging out the door.
A few details to the questions I can share:
1) The signaling, the SMIL generation and whole lot of other headaches from the MM* protocols are completely behind the API. We tried to keep this new feature as close to the SMS API you already know and love as possible - for inbound there are just four new params (NumMedia, MediaUrln, MediaContentType and the new unique identifier MessageSid) and for outbound just one new param MediaUrl.
You send / receive your photos - we make it work for whomever is sending or receiving. If you're at Twiliocon this week, two of our messaging leads Thomas Wilsher and Kelvin Law are dropping a killer talk on some of the technical details around this abstraction. It's probably my favorite of our talks at Twiliocon right now.
2) This was the combined effort of a whole lot of talent inside and outside Twilio for a very long time. Very proud of what they've been able to accomplish working together and so stoked to see first hand how excited developers are to use it.
3) This is real MMS sending and receiving pictures. We rolled out Picture Messaging first as we wanted to get it in developers hands as quickly as possible.
Got to head back out and join the Doers at the Design Concourse in San Francisco - Twiliocon only comes once a year, so I don't want to miss more time with all the hackers that came out to hang.
Always great to hear from you Josh. You should swing by if you're in town.