There is a good certainty that a Sprint phone is compatible with Verizon and vice versa. This is because they are both on the CDMA network. Although, if you do try to activate a Verizon phone on a Sprint account, they may not accept it due to it being on the Verizon network.
If the CDMA providers, like Sprint and Verizon unlock their phones so that they can be used on other CDMA networks, unfortunately, it doesn’t mean that someone can just contact their provider and have them activate the phone on their network. The Sprint Phones would have to be flashed with the appropriate image and then activated on the network. Where the problem comes in is if, for example, you have a Sprint phone that is unlocked and you want to activate on Verizon, but Verizon doesn’t sell the same model of phone. What that means is that there is no Verizon image for that phone and therefore, no way for them to activate it because the phone’s series of ESN numbers are not in their database. I believe that in the article you may have read, it stated “any compatible phone”. The key word is “compatible” and that basically means that the phone would have to be the exact same model that the carrier sells. Typically, Sprint and Verizon rarely sell the same exact model. Additionally, none of the data features would work, like MMS messaging or accessing the internet.
I’m afraid that people are thinking that using an “unlocked” CDMA phone on another CDMA network is going to be as easy as using a SIM-unlocked GSM phone on a different network, but I’m afraid that it really isn’t going to be that way. You are much better off using a Verizon phone on the Verizon network and same with Sprint.
Currently, if you want to activate a Verizon phone on the Sprint network or vice versa, it would have to be “cloned” and that is an illegal practice and if Sprint doesn’t sell the phone, you can’t clone it anyway cause there’s no ESN to clone it to. Get more info about Sprint available phones at sprintcustomerservice.org.