#blue is a web service to save text messages in an intelligent, searchable manner. It's a service of O2 UK, and sadly only currently available to O2 UK subscribers. However, it's a rather interesting web service, and it'd be great to see more service providers use a similar service. The fully functional #blue API provides a compliment to its web based service.
O2 has this to say about its API, on its developer site:
Welcome to the #blue API. With this API, client apps can, on behalf of users, do almost anything that can be done through the #blue website. This includes reading and sending messages, creating and updating contacts, and marking messages as favourites.
Its API is RESTful, and formats responses in JSON. It uses OAuth2 for authentication. With it, a developer can do pretty much anything one can do on the website. This includes reading a group of messages, reading a single message, reading account information, manage contacts or favorites, and send text messages. This means that a user could send messages from their computer as if it were their phone, which leads to many useful possibilities.
It would be great to see other cell providers start to offer similar services. If they started to advertise such things, and published APIs for them, developers could even make a truly universal chat client for smartpnhones, integrating text messaging and various internet chat services in a much more seamless manner. For more info, be sure to check out its developer blog.