History & peculiarities-
I normally don't post in revived threads from years ago and especially if the poster who revived it is a one off who read the thread randomly on the internet. However, the post touches on key aspects of voseo usage in Central America even though the commentary is brief it's precise.
The usage of vos as an alternate for t? in Latin America cannot be summarized collectively. I am sure those who have knowledge about its usage are clear regarding its distinctions. In Argentina, it's part of their vernacular as noted in my first post via the article and was only officially approved in 2006 by the RAE's affiliate and local language body la Academia Argentina de Letras as an official form. The usage is prevalent in El R?o de la Plata area of South America.
As the poster sonya1233 noted, the usage in Central America is unique. Collectively, as a region the usage amongst Central Americans (excluding Belize)- Guatemala, Honduras, El Salvador, Nicaragua and Costa Rica shows solidarity. Subsequently, the usage of 'vos' in each country individually has its own context. The poster clarified how 'vos' is used amongst Guatemalans and I posted a thread recently on the usage of 't?' in Costa Rica from Naci?n a Costa Rican daily newspaper. Clarification is needed as to the peculiarities of its usage in Honduras, El Salvador and Nicaragua. I have read some interesting details regarding Honduras and that 'vos' is used among family and good friends however, in my own experience with a few Hondurans that I have met that was not the case. Two months ago, I met a Honduran and his first question was 'de d?nde sos vos'. One example is not sufficient to draw conclusions but without knowing me other speakers would have used usted or t?. My experience with many Salvadoreans is very little usage of 'vos' and when used it's mostly at the end of phrases. Maybe with other Salvadoreans the usage is more prevalent.
The rest of usage heard in Latin America are in the partially voseo-speaking countries as mentioned in my post above. Countries where a segment of population uses voseo forms is evidence of vestiges of its usage that obviously have not been completed eradicated. This ties back to colonization, 'los virenatos' (viceroy) and centers of education in the New World. Depending on when Spaniards came to each Latin country changes in the language will have impacted the Spanish spoken there (in the New World). Peru and Mexico were large centers of education thus the eradication of 'vos'. In my experience, Peruvians do not use 'vos' in spite of what was posted above by one poster and definitely not Peruvians from Lima, an old colonial city that had a strong educational history. However, it may be possible in small towns far away from large cities. Colombia is an example too where it's used by a segment of population, mostly by departamento one can predict if 'vos' will be used. A friend of mine from Popay?n, (departamento- Cauca) uses voseo and t? forms but notably is more comfortable and instinctive with the 'vos' verbs forms. Once again the peculiarities differ by region and by country.
Those of you who know a bit about Latin American history should be able to make the connection regarding the Central American solidarity. This is not only a linguistic issue, clearly there a many linguistic similarities among the five countries, but it was a unified region at one point. Panama is a stand alone because it was part of La Gran Colombia before gaining it's independence as a country. As well, some will argue that since it's a bridge between the Atlantic and Pacific, is it really part of Central or South America. From a linguistic point of view, Spanish in Panama in a broad sense is not similar lexically to the rest of Central America. However, similarities do exist especially outside of Panama City and provinces close to Costa Rica namely Chiriqu?.
My standpoint regarding voseo is the usage is particular to speakers mentioned in the areas of above- R?o de la Plata, Central Americans and partially voseo-speaking countries. Although it was an approved as an official form in Argentina, it's not considered part of standard Spanish grammar. Spanish speakers from all regions understand those who use 'vos' forms, however, foreigners who desire to learn voseo verbs forms makes no sense. IMO, it's equivalent to foreigners in the DR who pick up the bad habits of vernacular speech as evidenced in many posts for example, 'mi do chele and 'qu? t?' piensa(s)' etc. There's definitely a fine line between wanting to sound local and sounding ridiculous.
I also recommend reading literature by Latin American authors, which clearly depict the vernacular language including 'el voseo usage'.
LDG/ MPLTA
One really popular one is A Dios le pido.