"Thanks for contacting Virgin Mobile Customer Care.
Regarding your previous email, let me inform you that Assurance customers can use any Virgin Mobile phone, it does not have to be the assurance issued phone.
They cannot use any Sprint phone or any other brand that is not Virgin Mobile. They won't be able to connect any phone. They will be able to connect only VIRGIN Mobile phones. They can use the phone from a previous Assurance wireless customer. As long as it is a Virgin Mobile phone they will be able to connect it. The ESN/MEID does not have to necessarily be the one assigned to the VIRGIN MOBILE account; they can use just any Virgin Mobile phone."
Just wanted to let you know that I'm currently researching this, and will post a thorough response once I've finished investigating. I've actually reached out to the Assurance team to ask them about their handset policies, and I will let you know what they say!