... just barely.
I have a Phantom Skin on my phone. I received my Seidio Innocase II today. I can confirm it does fit, but it's very very tight.
I would not recommend using both. The case started to pull up some of the edges of the skin. You basically can install the Innocase once if you're careful, but if you have to remove it to pull the battery, for example, you're going to mess up your skin.