I came across this article and found it pretty interesting:
It was always my understanding that Twitter did not allow buying/selling user names but it appears that, in this instance, a sale went through. A bit more digging revealed that Twitter (the company) was actually helping the sale go through.
Has anyone here successfully acquired and/or sold a Twitter account?
We have looked into it and when I did some research I came to the same conclusion that you did - that Twitter don't allow it.
Well the sale was made under the table so I think Twitter got nothing to do with it.
Yup, that sounds more like it...
You actually run the risk of being banned by Twitter (should they find out and choose to take action) as it's against their TOS.