There has been a lot of press about major companies twitter accounts being hacked and used to send out embarassing messages. If one is able to hack into any twitter account, such as a major brand, celebrity, politician, etc., especially one with 100,000's or 1,000,000's of followers, they could easily trick or encourage their followers to participate in a Telephony Denial of Service (TDoS) attack. For example they could take a negative position about a major financial organization and ask their followers to call a 1-800 number over and over. They could also trick followers into calling a number, 1-800 or whatever, to try to get tickets, concert passes, or some other "prize". For an account with 1,000,000 followers, 1% of the followers could generate 10,000 simulaneous calls - enough to seriously disrupt any target.
Here is a link to one article: