S4 won't come out on January. I can tell you that for the ff reasons:
1. For the past three years, Samsung has released the Galaxy S series in May-June, its like a schedule, like how HTC releases flagships on March, and Apple on September.
2. Even if the S4 does come out on January, you'd wait a long time for it since you are in the US and using carrier branded phones. The Note two 2 launched like almost 2 months ago and has been available every since. It means that IF the S4 does come out January, you'd have to wait until maybe April or June before it becomes available to you from your carrier.
My answer, get the best phone you can get now. An SIII or an Note 2 if you prefer. The SIII will get the multi app view in an update. Samsung already leaked a firmware for beta-testing with that feature. If you keep on waiting, you'll always here of something better to come. By the time an S4 comes out, there'd be rumors of an impending Note 3.