iPhone 8 and 8 Plus will be released by Boost and Virgin Mobile on September 29
While Sprint is launching the iPhone 8 and iPhone 8 Plus on September 22 (just like all other major US carriers), if you want to buy the new handsets from Boost Mobile or Virgin Mobile - Sprint's two prepaid brands - you'll have to wait an extra week to get them.
Both Boost and Virgin Mobile will release the two new iPhones on September 29, likely for the same prices that Apple is asking (iPhone 8 starting at $699, and iPhone 8 Plus starting at $799).
Boost and Virgin will also release the fancier and more expensive Apple iPhone X. While no launch date has been shared, the two MVNOs will take pre-orders for the iPhone X starting on October 27. It remains to be seen if they'll have the handset in stock on November 3 (when Apple and major carriers should launch it), or later.