Ting's blog, starting sometime in the afternoon next Tuesday Mar 11, it will finally be possible to activate to a used Sprint iPhone 5 on Ting. Although that doesn't sound very ground breaking, Sprint is very controlling about which phones they will or won't let their MVNOs activate. Up to now only Ting, Straight Talk and Net10 have been able to activate any iPhones and they have been limited to the iPhone 4 and 4S. As always, your iPhone needs to have a clean ESN, meaning that it hasn't been reported lost or stolen or flagged by Sprint for non-payment.
Ting's blog post also says that they will be offering the Samsung Galaxy S5 starting in mid-April for around $600, with the "All NewHTC One" arriving in May.
Ting is a no-contract postpaid Sprint MVNO that uses a unique tiered pricing model with prices stating at $6 per month plus taxes. For details about Ting's service and plans see Prepaid Operator Profile: Ting or visit Ting.com
Update 3/11/14: As promised, iPhone 5 activations are now working on Ting.