"Yup, messaging. Real, threaded, instant messaging.
Message other Tumblrs and they'll get messaging too."
Here is official wording from Tumblr...
"You’ve asked us for real instant messaging, and now it’s on its way. This means things like threaded conversations – yes!
Check out your dashboard for a little smiley balloon icon (if you’re using the app, be sure that you’ve updated to the latest version first). Click it to send a message to anyone. Your recipient will automagically get the messaging feature, along with your witty and uplifting message.
Not seeing the new icon? Have no fear, messaging will launch for everybody after a few weeks, giving us time to work out the kinks.
Once you have messaging, you’ll notice that fan mail has changed a bit. Old fan mail conversations can keep kicking, but you’ll need to use messaging for initiating outgoing gems."
Q: How do I get messaging?
A: You’ll receive the messaging feature when a friend who has it already messages you, passing it along. Everyone will receive messaging in a few weeks.
Q: Can I message any blog?
A: Almost! Private and group blogs can’t use messaging at this time, but other blogs are fair game.
Q: Can any blog message me?
A: Yep, though if you’re feeling bashful, you can toggle the switch in your blog’s settings on the web to only receive messages from Tumblrs that you follow.
Q: Can messages be anonymous?
Q: You mention fan mail changing. Will asks and submissions change, too?
A: No, you’ll still be able to use asks and submissions like always.
Q: Can staff turn on messaging for my blog?
A: We’re glad you’re excited about messaging. Our team can’t manually turn it on for you, though. Hang in there.