My experience with FreedomPop (I have 3 devices active with them right now) is that the Bring Your Own Device option only works with phone models they previously offered or are currently offering.
That means you can activate an EVO Design 4G, the original EVO 4G, and now the Galaxy S2 since they have just made that device available.
I've saw a list a few months back of 10 or so phones that were supposed to become available. One of them was the EVO 3D. I'm still unable to activate my Sprint EVO 3D with FreedomPop. I assume because they have not yet begun to offer that phone.
FreedomPop also uses WiMax as the primary connection (though their service does work over 3G if WiMax isn't available). I'm pretty sure the only phones that are going to be allowed to work with FreedomPop are old 4G WiMax devices.
Smart Phone History: Palm Treo650->HTC Faraday->Samsung Blackjack->Motorola Q->Nokia e61i->Apple iPhone 3G->HTC EVO->HTC EVO V->Moto X