I just bought a 10 month bull calf who ran through my hot wire and is now penned at my neighbor's place. I'm going over several times per day to get him used to me, but to no avail as of yet. He's still bellowing at me, pawing the ground etc. The pen is 10' x 20'. If he was in a bigger area, would it help to calm him down?

Yes, it would, preferably an area that has a much sturdier fence than a single or double strand of hot wire. First thing you didn't do right was train him on the hot-wire. Second was putting him in a place that wasn't going to hold him to allow him to settle in. Start by studying his flight or pressure zone when he starts reacting to your presence. In a 10' x 20' pen he can't get away from you, and he's acting in a way that is defensive to him towards you, the threat. Start by working with him from outside the pen, or the bigger corral, training him with pressure and release. Look up handling cattle by Bud Williams to get started on proper handling of cattle, which does not exclude bulls.