Well I went ahead and after talking to account services, I was able to use the upgrade tied to my airave to get the nexus s 4g and keep my primary line upgrade which I will be using for the EVO 3D. But just know that if you decide to do this, you need to speak to the right account services rep or else you will be screwed! The first one I talked to said it would be fine, I would just have a two year contract tied to my airave account. After picking it up at the store and getting it activated, I saw that the retail associate put my old evo onto my airave account, so I lost my airave and the free credit. I called sprint, got transferred to account services, and then the guy tells me they aren't supposed to upgrade based on the airave number and that I needed to return my nexus if I wanted my airave credit back. FINALLY I got a hold of the first person I spoke with and she went ahead and apologized and fixed everything. So it did work but it was a huge hassle so just make sure you have some time on your hands before you decide to do this!