The Pathfinder Core book states that and intelligent item uses & maintains its powers... but the legendary items description states that the bearer is the one that uses it.
This seems like common sense to me since legendary items are more powerful than normal intelligent items, but some of my fellow players are stating that legendary items do not use their own spell casting powers. That seems rather silly to me unless this is something specific to the "spell casting" ability, but even then those legendary powers are just emulating the normal intelligent items abilities.
According to the rules on intelligent items:
Unlike most magic items, intelligent items can activate their own powers without waiting for a command word from their owner. Intelligent items act during their owner’s turn in the initiative order.
All powers function at the direction of the item, although intelligent items generally follow the wishes of their owner. Activating a power or concentrating on an active one is a standard action the item takes. The caster level for these effects is equal to the item’s caster level. Save DCs are based off the item’s highest mental ability score.
From the rules on legendary items:
Spellcasting: This item allows its bearer to cast a limited number of spells as spell-like abilities. This ability can be taken more than once. Each time it’s taken, the bonded creature gains 5 points to spend on selecting what spells the item can cast. A spell costs a number of points equal to its level (minimum 1). The bearer can then activate the item to use each spell-like ability once per day. By spending double the cost, the bearer can use each spell-like ability three times per day. All spells must come from the same class’s spell list. No spell can have a level higher than the bonded creature’s tier. The caster level for these spells is equal to double the bonded creature’s tier. The save DC for these spells is equal to 10 + the spell level + the bonded creature’s tier.