Steve:
Although dropthezero is partially correct, (Porteños use vos in place of tu), his enthusiasm is a bit off. It's obvious he did not attend primary school in Argentina. The core grammar of Spanish has not changed in more than 400 years. Even though a 5 year-old Argentine intuitively knows to use vos instead of tu, he is still taught all six forms of verb formation in school because, despite what many think, Argentina is not culturally cut off from the rest of the Spanish-speaking world. Cervantes' famous work is still a mainstay in Argentine education as well as books by countless non Argentine authors. The stacks of books by non-Spanish authors found in bookstores and libraries have been translated into standard Spanish, not "lunfardo." Even La Nación and Clarín, the two main BsAs papers, publish in grammatically formal Spanish, voseo be damned. Therefore, if a 5 year-old Argentine has to learn to recognize all six verbal conjugations, it may be a good idea that you also learn them; if for nothing else, to distinguish between the written and spoken language. Then you'll be able to move about in most Spanish-speaking societies accomodating local regionalisms without depending upon expats from English-speaking countries giving you unneccesary advice and possibly pretending they have less of a gringo accent than you. However, here in Argentina you will not have a "gringo" accent but a "shankee" accent; even if you are from the United Kingdom.
Once you arrive in Buenos Aires it won't take you long to recognize and mimic the local dialect. For example, when I call my family in Méxcio, D.F. my mother always prefaces our conversations with "¿Qué pasó tu castellano?" as a reminder to speak correctly, the way as I was raised.
And that's don midlifebear to the rest of you