Like it or not, advertising is coming to Twitter.

One of the first advertisers to arrive was Los Angeles-based Ad.ly, which is promoting celebrity endorsements and representatives from business categories such as technology.

In the three months or so that Ad.ly has been in operation, it has signed up more than 10,000 “publishers” tweeting about a favorite product, Ad.ly co-founder and CEO Sean Rad says in this interview.

The idea that Twitter is defined as mostly conversation between friends is changing, says Rad.

“Conversation can  be content,” he says. “When it comes to Twitter, there is little distinction between what is content and what is a conversation.”

Ad.ly matches a “publisher” with a company, comes up with a per-tweet price for a celebrity or expert and analytics for both justifying the cost and effectiveness of an ad campaign. Advertisers can pick the celebrity and write the tweet ad copy which must be approved before it is broadcast.

Every advertisement is clearly identified as such in the tweet.

In this video, Rad explains in detail how he views Twitter, its evolution and the role his company plays as an “in-stream advertising platform” in pairing celebrity tweeter with advertisers.