Yep Best Buy has stopped selling the T-mobile Nexus S. No one knows why, it's probably because they ran out of stock and they are not getting anymore from samsung, hopefully in preparation for the Galaxy Nexus !!
They did stop selling them but they do have a bunch in their warehouse. I brought mine back to a Best Buy Mobile store for a rapid exchange this weekend. They are shipping a replacment to their store and should be here sometime this week.