Even though Jacob and all of the Quileute wolves from the Twilight series often refer to themselves as werewolves, they are actually shapeshifters. In Eclispe, when Bella visits the tribal meeting at La Push, Billy tells the ancient stories connected with the Quileute tribe:
"there has always been magic in our blood. It wasn't always the magic of shape-shifting--that came later. First we were spirit warriors" (244).
Jacob is able to change into a powerful wolf because of the 'magic' in his blood, magic that has reawakened since the Cullens' reappearance in Forks. For the Quileutes, their ability to transform into wolves is a defense mechanism built in to protect them from vampires. Unlike werewolves, shapeshifters' ability to change shape is not dependant on the lunar cycle. In most legends, people become werewolves because they were bitten by another werewolf, but Jacob, Sam, and the other boys become wolves due to a dormant 'magical wolf' gene in their DNA.
After reading the twilight saga series i'm fairly confident in saying that Jacob is a real werewolf and not a shape shifter.
Jacob is a shape shifter and his, as well as the packs, shape just so happen to be wolves. In Breaking Dawn when the fight is about to go down between the Cullen's and the Voltori Aro made it clear that Jacob and his counterparts were not werewolves since...
- They were born wolves the ones they fight against are made by biting a human just like vampire is made.
- They do not change un willingly and during a full moon
- Also silver bullets, any thing silver fro the matter, do little harm to the pack as opposed to the wolves the Voltori hunt.