The caster can activate the power as a limited free action instead of an action. The arcane skill roll is subject to multi action penalties as usual, but doesn’t cause any itself.

Thus, you could swing a sword (or take any other action) and cast a Hasty spell without a multi-action penalty. Taking two actions would cause the −2 multi action penalty to apply to both actions and the limited free action (the power does not contribute to the multi-action penalty, but it’s still affected by it).