We saw AT&T announce almost a week ago that they were receiving a variant of the Samsung Galaxy S called the Samsung Captivate. Yesterday, CellPhoneSignal wrote a story in which they claimed that the Samsung Vibrant is a Samsung Galaxy S variant destined for T-Mobile USA, and there may be a possibility of the phone launching on July 21st.
As for what sets this phone apart from the Galaxy S, AndroidandMe writes that "changes to T-Mobile’s version include a refined button layout. The touchpad is now gone and it has been replaced with four capacitive touch buttons" that may please some prospective buyers. Other than that though, it looks to be the same phone spec-wise, with all the major features there.
CellPhoneSignal also mentioned that the Samsung Vibran will come preloaded "with The Sims 3 game on board, Avatar, Amazon Kindle, GoGo in-flight Internet support, and an HD camcorder."
MobileCrunch notes that the reasoning behind the name is "likely in reference to the ridiculously bright AMOLED screen" of the device.
As for how the date of July 21st came about, TmoNews said that "we believe the Galaxy S is slated for a July 21st launch, though of course that’s subject to change. However, we know that the 21st is indeed slated for a two device launch."
No news on T-Mobile pricing either from what I saw.
Image from AndroidandMe