Follow the Money

Twitter doesn't charge members any fees, but really active Twitter members using mobile devices may get a bill from cell phone service providers -- most plans set limits on the number of text messages customers can send and receive. Twitter doesn't include advertising on Tweets or on Twitter Web pages, so it doesn't generate advertising revenue. In fact, the only way Twitter currently makes money is through private investments from venture capitalists. Twitter co-founder Biz Stone has even said that the company has no business plan [source: BBC].

Twitter on Your Cell Phone

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.

To learn more about Twitter and related topics, follow the links on the next page.