Any foreign-trained lawyer will have to take and pass a Bar exam in the State where he plans to practice. Some States allow foreign lawyers to take Bar exam after they got their LLM degree from an American university, for example. Check the rules with the Bar Association of the State where you plan to practice, as it varies by State.
In any case, one can't practice law in USA just because he is a lawyer in Colombia. As a minimum, one will need to get a License to practice law from the State in the USA.
Note: The above response is provided for legal information purposes only and should not be considered a legal advice; it doesn�t create an attorney-client relationship. For more information or to schedule a consultation, please visit http://www.law-visa-usa.com/contact_us.html