Altar calls are nothing more than religious traditions of men. As is true so many times, folks don't look to the Teacher for examples of 'altar calls'.....
Mat 9:9 And as Jesus passed forth from thence, he saw a man, named Matthew, sitting at the receipt of custom: and he saith unto him, Follow me. And he arose, and followed him.
No, can't be that simple can it? I've found that tradions of men usually outweigh the teachings of the Teacher.