in the office vs at the office

Jacob   Tuesday, January 13, 2004, 12:12 GMT
"In the office" means inside the office. "At the office" may mean inside the office, or just in the vicinity of the office.

So this sentence makes sense:

"I'm AT the office, but I'm not IN the office."
(Imagine a man on a cell phone in the parking lot outside the office).

But if you reverse the prepositions, the sentence doesn't make sense anymore; it's not possible to be in the office without being at the office.