Expo Mobile and ChitChat Mobile posted on their respective Facebook pages that they can now to activate the three iPhone models. Today EcoMobile confirmed that they can activate them as well.
iPhones will be allowed on other Sprint MVNOs soon. RingPlus has said that the Apple devices will be allowed no latter than March 27. A Kajeetrep told me that they don't support the iPhone yet but will in a week or two. Red Pocket Mobile is telling its dealers that iPhone support will be available April 1.
Of course the pioneer in iPhone support is Ting, which apparently has a special relationship with Sprint and has been accepting the iPhone 4 and 4S since Oct. 31 and the iPhone 5 since Mar 11.
Update 3/19/2014: RingPlus and Good2Go are now activating the Sprint iPhone 4, 4S and 5.
Update 4/9/2014: Kajeet has confirmed that they can now activate iPhones.
Update: Sprint Will Soon Allow The iPhone 4, 4S and 5 On RingPlus, Possibly Other MVNOs
Use You Own Sprint iPhone 5 On Ting Starting Mar 11
Updated: Effective Nov 15, Sprint to Block Its MVNOs from Activating Galaxy S4, HTC One, Note 3 and Others
Sprint MVNO Ting Now Acivating BYOSP iPhones
Sprint and Sprint MVNO Prepaid Plans Compared