
Jeraa |

I have a player who is a barbarian and wants to multiclass into a spell-casting class, when he rages it says he cannot use and charisma, dexterity, or intelligence based skills, so is spell-casting considered using a skill?
No, a spell is not a skill in any way, shape, or form. But as Cataphor pointed out, there is another part of that sentence that prohibits spellcasting while raging.

Void Dragon |

okay so here is my second and third question the spell rage says that this spell is identical to a barbarian's rage so this would also prevent spell-casting correct?
3) what if they had an item that granted the class feature rage would this case prevent spell-casting
(only reason I want to know is the barbarian is thinking of making rage granting items for rest of party and then just having everybody rage.)

Jeraa |

okay so here is my second and third question the spell rage says that this spell is identical to a barbarian's rage so this would also prevent spell-casting correct?
3) what if they had an item that granted the class feature rage would this case prevent spell-casting
(only reason I want to know is the barbarian is thinking of making rage granting items for rest of party and then just having everybody rage.)
It doesn't matter what the source is - if an ability grants rage that works like the barbarians rage then the same restrictions apply.
The Rage spell specifically states it works like the barbarians rage, so while the spell is in effect, no other spells could be cast.