While I can totally relate to this poor guy finally reaching the breaking point, this could have all been avoided.  Since probably every cube-dweller works near someone like this, maybe we can all sort of come together and agree on a few simple rules to make life better for us all:

1. Never ever use speaker phone in an open office.  I know it's a pain to actually pick up the receiver, but you never know when that guy next to you is going to finally crack.
2. When using the phone in an open office, use your "inside voice."  Yes, your voice does carry. 
3. If you need to make personal calls, go outside.  Your personal life really isn't that interesting to your coworkers.

Believe it or not, 81% of supervisors don't think noise is a problem for their workers.  Maybe someone should explain why noisy coworkers cost them money.