As soon as the recording starts, Sam opened his mouth to speak. There were hundreds upon hundreds of things he wanted to say to Dean, starting with apologies and ending with farewells. He wanted to apologize for Dean's death, he wanted to apologize for lying to him for so long, he wanted to apologize for running away, he wanted to apologize for the demon blood, and finally, he wanted to say good-bye. Because Sam might have been powerful enough to take Lilith on with all of that demon blood running through him, but even he couldn't predict how his encounter with her was going to end.
He had so much that he wanted to say to him. But Sam suddenly found that he didn't have a voice to lend to those words.
Stop checking your damn phone. He's not going to call you.
Ruby had been right. Sam quietly flipped his phone shut, leaving the message a silent one.