Any Boost, Virgin or Sprint Prepaid phone that hasn't been used as a Boost, Virgin or Sprint Prepaid phone for at least 12 months will no longer be allowed to be activated on any Sprint MVNO.

Boost, Virgin or Sprint Prepaid phones that are currently active on a Sprint MVNO will be grandfathered and can remain on that MVNO indefinitely, provided they are never deactivated .

. Boost, Virgin or Sprint Prepaid phones that were deactivated from a Sprint MVNO can not be reactivated on any Sprint MVNO unless they were used on their respective Sprint prepaid brand for 12 months.

I think plan changes will be OK for grandfathered phones but phone swaps and probably phone number changes will cause grandfathered phones to get deactivated.

There should be no changes to the rules for postpaid phones. They have to be free of any financial obligation to Sprint to be used on an MVNO. That means fully paid for, out of contract, no EIP payments due and not last used by a customer whose account is suspended for non payment.

Sprint network capable iPhones and Nexus Phones purchased at full price from the Apple Store or the Google Play Store should still be usable immediately on Sprint MVNOs.

Effective April 17, 2016, Sprint will no longer allow new, never activated Boost Mobile, Virgin Mobile or Sprint Prepaid phones to be activated on Sprint MVNOs. The struggling CDMA carrier will make a change to its MVNO activation system that result in the rejection of any phone from its Boost, Virgin or Sprint Prepaid brands unless said phone has been used at least 12 months on the Sprint prepaid brand it was sold for. The change was announced by RingPlus CEO Karl Seelig in a forum post today.As Seelig points out in the post, this is not a policy change by Sprint but the closing of a loophole. Prepaid devices were always supposed to be blocked from MVNO activation until they had been "aged" for 12 months on their original Sprint prepaid brand. But Sprint's MVNO device activation software, whether by accident or design, would allow brand new prepaid devices to be activated provided the phone had never been activated on the Sprint prepaid brand it was intended for.The loophole seems to have been introduced shortly after Sprint revised their rules for MVNO activation last February to start allowing prepaid phones on MVNOs after 12 months aging. Before that change, Sprint's prepaid phones were completely blocked on MVNOs.As word of the loophole spread I'm sure many thousands of inexpensive Boost or Virgin Mobile phones like Moto E's or LG Volts were activated on Sprint MVNOs. The unlocked GSM version of the 2nd generation Moto E LTE lists for $120 and even now, near its EOL, goes for $90 on Amazon. Boost, On the other hand, Virgin and Sprint Prepaid Moto E's are widely available for $30 or $40 from big box stores. With the closure of the prepaid loophole the supply of inexpensive phones for Sprint MVNOs is likely to dry up. That could mean slower growth for Sprint MVNOs, especially ones that depend on BYOP, like RingPlus. FreedomPop has always relied more on selling attractively priced, mostly postpaid, pre-owned Sprint phones that have been cleared for MVNO so they will probly be impacted less.Based on Karl Seelig's post, I think the post-April 16 activation situation on Sprint MVNOs will look something like this:Of course what really matters is not what Sprint says the rules are, but how new rules are implemented in software. The changes Sprint made last February were very buggy when first introduced and blocked the activation of large numbers of phones that should have been eligible. Once again, anything could happen. If you have a phone, prepaid or not, that you want to use on a Sprint MVNO, I recommend activating it before April 17 to avoid the chaos that's likely to follow Sprint's rule change.Image: Pixabay