Twitterfone launched in May to let Twitter users post new messages by calling in to a phone number and speaking out what they want to say. The service then converts the message to text and posts it to your Twitter account along with a link to the audio file. Here’s a test message I created at the launch. The service is a great way to leave a quick Twitter message when you’re away from your computer and only have access to a phone – the service offers local number in 19 countries and is expanding regularly. The company says 20,000 people have signed up for the service since launch.

Today Twitterfone will start converting your Twitter messages to audio, too, giving users a full audio interface to the service. As of today, when you call Twitterfone the service offers to let you record a new message, listen to messages from your friends, and reply to messages publicly or privately. Users can listen to the first ten messages.

For now, only English is supported, but Japanese is next up. The service is free and will remain so for the foreseeable future.

If you are a Twitterer, you’re gonna love this. Below is a quick demo video I did via Qik that shows the functionality.

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.

A number of services have launched to allow users to record messages and link to the recording from Twitter (see Twitsay, Twittergram). And services like Jott and Spinvox are providing tools that allow voice to text conversion for Twitter, Facebook, Pownce and other social networks. But nothing I’ve seen so far is as simple to use as TwitterFone, a new service by serial Irish entrepreneur Pat Phelan.

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 (here’s a test message I left). 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 partially automated via voice recognition software, and flagged words go to a human for translation. For now the service supports English only; Japanese support is promised in 8 weeks or so.

One problem/slightly humorous aspect of the service is that there is no going back once you start recording. In this test message I started coughing and just hung up. The coughing was dutifully transcribed and posted. A simple option at the end of a call to delete the message is needed.

The service is free for now, they may add premium features over time. We have a handful of beta accounts to give out now. Tell us why you think you need it in the comments below – the most compelling get an account.