Shawn Blanc posted two links to interesting posts which have more speculation related to possible Twitter integration into iOS 5 system-wide. The first link is to a post by Anil Dash who writes:

But in short, the hardest, most expensive technical part of building a web-scale Twitter competitor already exists in Apple’s infrastructure. What’s missing, in an odd reversal of Apple’s usual pattern, is a well-designed, simple user experience that makes people want to participate. Could a small team of developers and designers within Apple make a credible realtime messaging service with first-rate native clients on every important platform? Could they graft on a simple, REST-based web-style APIs to the complicated, old-fashioned API that enables push notifications right now? It'd be a lot like building a usable, delightful user interface on top of well-established, but complicated, technological underpinnings, wouldn't it? I wonder if Apple has those skills. The other post Shawn links to is by David Silva, who writes: Look at the way Android integrates both Facebook and Twitter into its OS. With that system wide integration I can now scroll through my contact list, see a pretty avatar that is automatically pulled from my friends accounts and also read/reply to recent status updates as well as browse through all of their Facebook pictures all from within the contact card. He later speculates on the specifics Apple could expand on: * DM and @reply options from within your contact card just like FaceTime, text email and call. * Tweet pictures and video direct from the Camera app. * Read and write Twitter DMs direct from the “Messages” app just like regular text messages. * Twitter avatars in your Contacts cards.