Why not do a collaboration with Necuno Solutions? They are already doing a collaboration with Maemo Leste (https://necunos.com/blog/necuno-solu...collaboration/) and Nemo Mobile (https://necunos.com/blog/necuno-solu...collaboration/) so they could probably help creating the Neo900!
Otherwise there are other open smartphone manufacturers that may be interested like Jolla, Planet Computers, Turing Phone and Purism.