https://www.cnet.com/news/samsung-galaxy-s-2010-original-was-a-confusing-mess/

Importantly, the first Galaxy S wasn't a single phone. Though it landed at all big four US carriers around the same time, it was split into four personalities, one for each carrier. These names sounded straight out of a motivational seminar (the Captivate! the Fascinate!) and features varied slightly between the models. 

Sprint's phone went so far as to add (gasp!) a physical keyboard, while the other three were candybar designs. It was a thing carriers did at the time -- stand apart from your rivals by marketing a unique device that only you had -- but the result was a perplexing experience for customers. (Overseas customers had it easier -- it was just called the Galaxy S.)