Which acronym represents the service that enables sending short text messages?

The acronym that represents the service enabling the sending of short text messages is SMS, which stands for Short Message Service. This service is commonly used for transferring brief text messages between mobile devices. Introduced in the 1990s, SMS has become a foundational component of mobile communication, allowing users to send messages that can include text, numbers, and sometimes multimedia content in a quick and efficient manner.

In contrast, the other acronyms represent different concepts: USB stands for Universal Serial Bus, which is a standard for connecting devices and transferring data; SEI could refer to various entities but is not related to messaging; and PST typically stands for Personal Storage Table, a file format used by Microsoft Outlook for storing emails, contacts, and other data. Thus, SMS is clearly the correct choice for the service focused on sending short text messages.