"Oh god, what a question...", I thought, but then realized it's not that simple (even if not meant that way):
The question is not: "What's 'im'?"
The question is: "When do you use 'im' and when do you use 'in'?"
The preposition "in" alone can never be replaced by "im". Only in combination with "dem". None of the answers mentioned that. Let's say the asker understands that that's apparently the case.
Furthermore, "im" cannot always be replaced by "in dem" and vice versa. See answers.
One could argue that this should be obvious from even a little bit of research, yet not even all renowned dictionaries manage to capture this fine little difference. On PONS "im Januar" is subsumed under the categories "in = in dem" and "sich dort befindend".
My 2400 page thick Duden-Oxford dictionary lists dozens of examples but does not mention incommutability => It's not a dictionary question.
Research effort (online) certainly can't be a close reason. Do you really think we should not answer questions that have been "solved" on Yahoo or the like?
Lastly: Even if a question is not that great, we should answer it and encourage the asker to show more effort next time. Why? Because we have like one question per day.
Seems perfectly on-topic for me, so why close it? It would be a nice addition to our SE.
Edit: Just look how much (mostly positive) turmoil this question created, another reason not to close it.