My first line of this post was going to read: "The time has come after four years of operating as a business, Twitter has hired a PR person. I saw the news this morning on the Read Write Web blog."
Then, I read to the bottom of said post on RWW and it identifies at least three other comms department staffers inside Twitter already. That happened pretty quietly... and based on RWW's feelings they need more and better PR still:"Twitter desperately needs communications help. The company has grown in importance faster than it's been able to keep up with. Garrett's phone will no doubt be ringing off the hook. He'll be working in the Communications Department with Jenna Sampson, who came from Yahoo!, former CNN correspondent Alexa Lee and Emily Pinkerton, among others. You can follow all four on Twitter via this list."
So Twitter's new Vice President of communications is a chap called Sean Garrett, a founder of 463 Communications. His announcement is here on his blog. I've worked agency-side for a number of social media hot-houses so will follow their PR growth with great interest.