Boost Mobile

Hm... looks like they have another promo now...

4 lines $100

Unlock Policy!/support/faq/phones-devices/unlocking-policy/

I guess a way to get 4 free phones, then swap in your current phone and request DSU.

free Alcatel Dawn, LG K3, Kyocera Hydro Reach, LG Tribute HD, Samsung Galaxy J3 (2016) or Samsung Galaxy J3 Emerge (2017 Android phone or a discount on a higher priced phone. Discounted phones include a $29.99 LG X Power, $99.99 iPhone 5s 16 GB, $199.99 iPhone SE 16 GB and a $249.99 iPhone 6 16 GB.