One of the things Whisper had was a method of encrypting SMS messages so they still fit in an SMS message, perhaps Twitter is hoping to take advantage of that?

I can't imagine Twitter developing a product that prevents them from being able to look at Tweets going through their system.

This is why I think this is such a strange move on Whisper Systems part. Their products are all about privacy. Twitter wouldn't have a business model if they gave their users proper privacy.

Well, I can see a company about to sink (RIM) and leaving a big empty space for a smart move here. If twitter can take that space and provide enterprises and people along a way to exchange encrypted messages painlessly, that'll be perfect.

Social media is said to play an increasing role in revolutions and social movements; there's clearly something to do. Perhaps even, let's be audacious, some money to make.

Note: I don't actually think RIM is quite dead yet.

Think Egypt, Syria, China: countries where large-scale keyword filtering and MITM attacks are common, and the infrastructure is owned by the opponent.

What's needed in those cases isn't peer-to-peer encryption, but peer-to-service (and service-to-peer) encryption: tweets encrypted on the device, sent, and decrypted on Twitter's servers; timelines sent encrypted, and decrypted client-side.

Twitter still gets plaintext, but intermediaries can't trace/target pseudonymous users (or filter content).

This could be a real edge for Twitter in countries (China) where they're losing ground to monitored/censored clones (Weibo).

tl;dr: They're probably building Tor, not Skype/BBM.

Twitter already has client-to-service encryption with their https APIs.

Could there be a patent in play perhaps?