In many/most jurisdictions there is a statute of limitations against collecting debts and ownership of property both chattel and real estate including a 'loaned' dev phone. That means after a few years there is no way to enforce the deal and so you can throw away or recycle/reuse(sell) the item which has been abandoned in your possession without any action by the owner acting like they still own the device.
Possession is sometimes called 9/10ths of the law and eventually it actually becomes presumed to legally be yours without legal remedy to a person or company who has abandoned the object or property.
IANAL so if you are really worried consult a lawyer or if you know the details of your statute of limitations law just consider it abandoned and enjoy your rights to do whatever you like once that statute of limitations has expired no matter what the sticker on the phone says.
Think of it like an old automobile that a friend leaves parked at your house, after disappearing for maybe three, seven, even ten years depending on the law you can have it towed away and recycled or sold to free up your parking area without fearing a lawsuit later, you do not have to guard this item forever.
I forget now, when did the N950s get loaned out?
Also remember that no matter the law a tight knit community like TMO where a few N950s were gifted/loaned to the top devs there will be jealousy and bad feelings when the not-gets see you selling your phone. You will hear whispers and shouts about you breaking a sacred oath to forever develop for this platform when you bound your soul to this N950 amulet.