Tower Shield Bash
A tower shield bash is treated as a melee attack with a two-handed weapon.
A tower shield bash deals 1d10 points of bludgeoning damage.
A tower shield bash is not subject to the penalty on attack rolls that is caused by the tower shield's encumbrance.
A tower shield bash cannot be used in order to perform a full attack (regardless of how high your base attack bonus is).
FAQ
Q: After performing a tower shield bash, do I lose the shield bonus that is provided by my tower shield until my next turn?
A: No.
Q: If my tower shield has an enhancement bonus, should I apply that bonus to my attack & damage rolls when performing a tower shield bash?
A: Yes.