OK, so here’s the text in question:
Spell Rage (Ex)
A rage mage can cast spells while in a rage, as long as the spell’s casting time is no more than 1 full round. When she casts a spell of the abjuration, conjuration, evocation, necromancy, or transmutation school while in a rage, the rage mage uses her character level as her caster level. This ability only works when the rage mage is in a spell rage.
While in a spell rage, a rage mage becomes reckless and loses her some of her ability to defend herself. She temporarily takes a –2 penalty to Armor Class. She can attempt Concentration checks to avoid having a spell disrupted, but can’t use any other Charisma-, Dexterity-, or Intelligence-based skills (except for Balance, Escape Artist, Intimidate, and Ride) while in a spell rage.
A fit of rage lasts for a number of rounds equal to 3 + the character’s Constitution modifier. A rage mage can end her rage voluntarily. At the end of the rage, the character is fatigued (–2 Strength, –2 Dexterity, can’t charge or run) for the duration of the current encounter (unless the rage mage is 10th level, when this limitation no longer applies). A rage mage can only fly into a rage once per encounter, and only a certain number of times per day (determined by level). Entering a rage takes no time itself, but a rage mage can only do it during her action, not in response to somebody else’s action.
Effectively, Spell Rage is a separate effect that has to be activated separately from Rage, and uses a different pool of uses. Since both are activated as free actions, you can always activate both at once to gain the benefits of each. Note that Spell Rage specifically allows you to cast spells during a normal Rage, overwriting the usual restriction in Rage that prevents that.