Twitter is certainly usable via SMS on a mobile device, but typing messages on a phone is cumbersome. A service that converts voice to text and then posts it to Twitter could be a niche hit. The service launched moments ago into private beta. To use it you need to verify your phone number and Twitter account, and TwitterFone will then give you a local phone number to call to leave messages (they support the U.S., UK and Ireland now, adding more). Then, any message you send will be transcribed, and posted to Twitter along with a link to the recording. If the message is longer than 140 characters, just the first part is transcribed, but the entire recording is still available. There is a time limit of 15 seconds on the recording. The service is free for now, they may add premium features over time.