Many social networking Web sites have lots of bells and whistles. Sites like MySpace and Facebook let users build profiles, upload pictures, incorporate multimedia, keep a blog and integrate useful or bizarre programs into homepages. But one Web company with a very simple service is rapidly becoming one of the most talked-about social networking service providers: Twitter.

So what does Twitter do? When you sign up with Twitter, you can use the service to post and receive messages to a network of contacts. Instead of sending a dozen e-mails or text messages, you send one message to your Twitter account, and the service distributes it to all your friends. Members use Twitter to organize impromptu gatherings, carry on a group conversation or just send a quick update to let people know what's going on.

Twitter's history is entwined with a few other Internet companies. Twitter's founders are Evan Williams, Biz Stone and Jack Dorsey. A few years before Twitter was born, Williams created Blogger, a popular Web journal service. Internet giant Google purchased Blogger, and Williams began to work directly for Google. Before long, he and Google employee Stone left the Internet giant to form a new company called Odeo.

Odeo is a podcasting service company. According to Williams, he didn't have a personal interest in podcasting, and under his guidance, the company temporarily lost focus. However, one of Odeo's products was just beginning to gather steam: Twitter, a new messaging service. Stone gave Twitter its name, comparing the short spurts of information exchange to the chirping of birds and pointing out that many ring tones sound like bird calls [source: San Francisco Chronicle].

As the service became a more important part of Odeo, Stone and Williams decided to form a new company with Twitter as the flagship product. Williams bought out Odeo and Twitter from investors, then combined the existing company and service into a new venture called Obvious Corporation. Jack Dorsey joined the team and began to develop new ways for users to interface with Twitter, including through computer applications like instant messaging and e-mail. In March 2006, Twitter split off from Obvious to become its own company, Twitter Incorporated.

In this article, we'll learn about Twitter's application programming interface (API). We'll find out what a Tweet is and all the different ways you can create and read them. We'll also look at how Twitter can interact with mobile devices like cell phones.

In the next section, we'll learn what, exactly, a Tweet is.

Simply put, a Tweet is a message sent on Twitter. To send or receive a Tweet, you have to create a free account with Twitter. You also need to have friends and contacts with Twitter accounts -- otherwise you're typing to the void. Of course, you could use Twitter as a blog and keep all of your Tweets public, meaning anyone could read them on your personal Twitter profile page. But if you want to use Twitter as a way to keep in touch with friends, you'll need to convince them to sign up, too.

Once you have an account, you can begin building your network of contacts. You can invite other users to receive your Tweets, and you can follow other members' posts. As you receive Tweets, you may discover you're looking into only part of a conversation. You'll see your contact's posts, but if he or she is sending messages in response to someone who isn't in your network, you won't see the other person's messages.

Tweets have a few limitations, mostly due to the fact that Twitter's design relies heavily on cell phone text messages. Tweets can only have up to 140 characters before the system cuts off the rest of the message for cell phone users. Members can read full Tweets on their Twitter Web pages or by using a third-party developer's desktop or Web-based application.

Tweets can only contain text -- members can't include pictures, video or other computer files with Tweet messages. Members who want people in their network to look at multimedia content must find a Web page to host the files, then send a message containing the page's address to their networks. Twitter converts all addresses more than 30 characters in length into tiny URLs -- links that compress the full Web site address to conserve space.

Twitter makes it easy to opt into or out of networks. If you join Twitter and find that you're being bombarded by Tweets from a particular member, you can choose to stop following his or her feed. All you have to do is send a message to Twitter that says "off," plus the chatty member's user name. Later, if you find that you miss the sender's updates, you can type "follow," plus the user's name. As long as the sender has kept you in his or her network, you'll start receiving those messages again.

Twitter bases its application programming interface (API) off the Representational State Transfer (REST) architecture. REST architecture refers to a collection of network design principles that define resources and ways to address and access data. The architecture is a design philosophy, not a set of blueprints -- there's no single prescribed arrangement of computers, servers and cables. For Twitter, a REST architecture in part means that the service works with most Web syndication formats.

Web syndication is a pretty simple concept: An application gathers information from one source and sends it out to various destinations. There are a few syndication formats used on the Web. Twitter is compatible with two of them -- Really Simple Syndication (RSS) and Atom Syndication Format (Atom). Both formats retrieve data from one resource and send it to another.

Both Web syndication formats compatible with Twitter consist of a few lines of code. A Web page administrator can embed it into the code of his or her site. Visitors can subscribe to the syndication service -- called a feed -- and receive an update every time the administrator updates the Web page. Twitter uses this feature to allow members to post messages to a network of other Twitter members. In effect, Twitter members subscribe to other members' feeds.

By allowing third-party developers partial access to its API, Twitter allows them to create programs that incorporate Twitter's services. Obvious Corp's applications include desktop feed reader programs that let users post and retrieve messages on Twitter's network using a simple, independent interface. Current third-party applications include:

That's just a small sample of Twitter applications available, and developers introduce new ones every day.

In the next section, we'll look at technical side of Twitter -- how it interfaces with mobile devices.

From the beginning, Twitter's founders designed the service to work with the Short Message Service (SMS) protocol. SMS allows you to send and receive text messages from a cell phone to other phones and services like Web sites, voice-mail systems and e-mail servers. When you send a text message from your phone to Twitter, the message transmits to a mobile switching center (MSC), which sends the signal to a signal transfer point (STP). From there, the message goes to a short message service center (SMSC), which then sends the text to Twitter. Twitter sends the message back out to the people in your network using the same process in reverse.

The SMS protocol has several restrictions, which are the source of Twitter's limitations. An SMS message has an upper limit of 160 characters and can't include anything other than text. While there are other protocols that can send more information than SMS, they aren't as widely supported by cell phone service providers. By limiting messages to the SMS format, Twitter is able to reach a larger customer base.

One potential headache for Twitter is SMS spoofing -- a technique that allows someone to post messages from another person's cell phone number. In the early days of SMS messaging, this was pretty easy to do: Many cell phone service providers allowed people to send messages from an online form to a cell phone. One of the fields in the form was "from," and people could put anything they wanted in the field. A mischievous person could enter your phone number in the "from" field and send a message to Twitter. Your Twitter page would receive these fake messages -- as would everyone in your network -- as if you had legitimately posted them. There aren't many sites that allow this kind of messaging anymore, but several Web pages specifically designed to spoof SMS messages have appeared. Spoofing hasn't become a big problem on Twitter yet, but if that changes, the company may have to look into ways to prevent it in the future.

Twitter will also send messages over SMS to cell phones even if you use a desktop or Web-based application to post your Tweet. When you post your message, you tell Twitter to send the message out to all the appropriate outlets through the syndication format. Twitter sends the Tweet out to the cell phones of anyone in your network who has added a cell phone number to his or her Twitter account. For other users, the message may only appear on a Web page or in a computer desktop application.

Twitter members in the United States can interact with the service through their cell phones by sending text messages to 40404. In Canada, the code is 21212, and in the United Kingdom, you'll give your fingers a workout with the code +44 7624 801423. Through text messages, you can subscribe to other members' feeds, turn off feeds, add friends to your network or even delete your account.

Twitter's popularity appears to be on the rise. While the company hasn't found a way to monetize its services yet, many think it's only a matter of time before it finds a way to make Tweets profitable. Even if the service never turns a profit, it has served as an important role in online social networking -- what many Internet experts see as the future of the Web.