Long codes are meant for person-to-person communications, and can send only 1 message per second. For high-volume, application-driven messaging, Twilio recommends using a short code. Short codes can send SMS and MMS at 100 messages per second, and this high throughput is perfect for applications needing to send time-sensitive messages to many users at once. Furthermore, since carriers vet and approve all short codes for their intended use, they are not subject to carrier filtering or suspension for heavy traffic.
Examples of applications best suited to a short code include: marketing communications, large one-to-many notification bursts, and high volumes of one-to-one transactional notifications.
If you have questions about which number is right for your application, please contact Sales.