Open Twitter, allow anyone to be a Twitter server, and sell their services to Twitter providers who don't want to deal with Twitter nuts and bolts, as Disqus does for comments and Google does for gapps.

Be an expert in Twitter and sell training to implementers and users, as GitHub does for git.

Have free and paid levels, as GitHub, Disqus, Dropbox and countless others do.

Have all paid services, as old school businesses do.

There's probably more else that I haven't covered.