Twitter chose the five-digit SMS short code 40404 for memorability.
Twitter was designed around sending and receiving short status updates by text message, so selecting an easy-to-remember SMS number was an important early product decision. Developers initially considered 10958, but later replaced it with 40404 because the new number was easier to use and remember.
The five-digit format also influenced the service’s early branding. The original project name, “twttr,” had five characters, echoing the length of common American SMS short codes. This helped connect the name, the mobile technology, and the service’s deliberately compact identity.
The code was part of Twitter’s early U.S. SMS experience, not a universal number for every country or every later version of the service. As Twitter expanded, people increasingly used the website and mobile applications instead of text messaging. The service eventually discontinued SMS functionality in most countries in 2020 after security vulnerabilities were exposed. The number 10958 is therefore a plausible distractor: it was an earlier candidate, but 40404 became the memorable code associated with Twitter’s launch-era messaging system.