I have corrected many a sentence with a terminal preposition. “Where are you at?” becomes “Where are you?” and “What do you need the telephone for?” becomes “Why do you need the telephone?”.
But if you were taught that ending a sentence with a preposition was a hard and fast rule of English grammar, you only heard half the story. Though many times, we should correct terminal prepositions, sometimes doing so makes the sentence more unwieldy than it should be.
Consider this sentence, “I like the company I work for.” Should we correct it to say, “I like the company for which I work”? Doubtful. (Most likely, I would avoid this altogether and write, “I like working for my company.”)
There are historical and technical reasons for the evolution of this rule, but it can be solved simply by focusing on communication. If you find yourself doing linguistic gymnastics to avoid ending in a preposition and the resulting sentence is convoluted and pretentious, abandon the enterprise. Write simply and clearly.
Winston Churchill was famously criticized for occasionally using a terminal preposition, to which he replied, “This is the type of errant pedantry up with which I will not put.” Well said.