You know Dean called Billie because it was killing him not knowing about Sammy. I think it wouldn't have bothered him half as much if him and Sam could talk through air vents or something. And I would not be surprised if the plan all along was for him to sacrifice himself so Sam can be free. They should his blood Deal with Billie, not Sam's.
And if something went wrong...well they were both dead together.
THESE TWO!
