(portable) internet in Berlin?

Heya,
I'm freshly arrived in Berlin and a friend of mine told me about these wonderful inventions for w-lan access. I assume from his description they are like USB sticks and can be purchased for around 25 euros a month, plugged into your laptop, and henceforth provide you with endless wireless internet brilliance. Is this true? I asked my cousin (a native Berliner) but she had only vaguely heard of such a thing, and my germlish is still a bit too rusty to ask technologically astute questions to an internet provider.
I'm doing freelance work from afar, so think this is a better option than being at the mercy of w-lan cafes. All advice is much appreciated!