On June 26th 1963, President Kennedy arrived to Berlin after visiting Bonn, Cologne and Frankfurt, where he had given speeches to huge, wildly cheering crowds. During his eight-hour visit, he gave a speech to an immense crowd gathered in the Rudolph Wilde Platz near the Berlin Wall to deliver a speech with now famous ending.
‘Two thousand years ago the proudest boast was “Civis Romanus sum.” Today, in the world of freedom, the proudest boast is “Ich bin ein Berliner.”‘ According to the urban legends [probably started by Len Deighton spy novel Berlin Game] Kennedy allegedly made an embarrassing grammatical error by saying “Ich bin ein Berliner,” referring to himself not as a citizen of Berlin, but as a jelly doughnut. In fact, he didn’t. It was grammatically correct.
However, Kennedy did not speak German, so to pronounce the sentence, he wrote in his note, “ish bin ein Bearleener,” in phonetics.
Correctly, you would say
Ich bin aus Berlin – I am from Berlin.
Actually, it is grammatically incorrect. To say you are a Berliner or a Stuttgarter, you do not use the pronoun “ein” (a). You drop it. So you would say “Ich bin Berliner” or “Ich bin Stuttgarter.” “Ein Berliner” is a doughnut. Just like “ein Frankfurter” is a hot dog.