From the 3.5 FAQ:javcs said:
"Incorporeal touch attacks and touch attacks aren’t
the same thing. If they were, they would not have different
names.
An incorporeal touch attack actually resembles a slam
attack (battering the foe with a fist or other appendage), except
that it passes through physical armor or shields. The term
incorporeal touch attack simply serves as a reminder that most
armor bonuses aren’t effective against these attacks.
Armor and shield bonuses from force effects, such as the
mage armor spell, shield spell, and bracers of armor are
effective against incorporeal touch attacks, as is ghost touch
armor or a ghost touch shield.
Like a ghost touch weapon, an incorporeal creature or
manifested ghost can wear ghost touch armor and get an Armor
Class benefit from it. Such a creature also can pass through
solid objects while wearing ghost touch armor."
