Unlocked Sprint phones you can activate on Boost

 They update the list periodically, you can check it out here:  Activate A Sprint phone . 

You can contact our Social Care team on Facebook Messenger just click the icon below, to unlock your Sprint phone for Boost.

The unlocking policy section says the Samsung S7 "Special Edition" can be used, but I'm not understanding what the special edition means? Would getting an unlocked S7 directly from Samsung work on boost? 

From what I have read. Is the GS7/Edge "Special Edition" = Unlocked version purchased from Samsung direct.

Not a Sprint branded version.

If you look at my reply here, you'll see the link.  We probably won't know about the S8 until it's live on the site.  We are now offering it on Shop.

To unlock your device you would need to meet with some requirements. The person requesting the device to be unlock, must be a current or former customer or an individual owner who can provide the phone number and pin code for the account last associated with the device.
The device has not been reported as lost or stolen. The device has been activated at least 12 months and a payment was been made within the last 90 days of that 12-month activation. Victor21

Mostly it is about the phone model and not the carrier, to be safe you should take it to a store and have it checked. Click here to read the information on bringing your phone to Boost.