Not only do Argentines prefer the spoken word over the written word, they also prefer face-to-face meetings to telephone conversations. This means that by far the best way to develop good business relations in Argentina is to take the trouble to visit people. (However, one complication here is that it can be quite difficult to get people to commit to meetings very much in advance as they prefer to be able to manage their time on a week by week, day by day basis!)
Meetings will usually start with a long pre-meeting chat which will cover topics as diverse as football, weekend activities and holidays but which is unlikely to include any mention of business. You can also expect a fairly lengthy repetition of this type of conversation at the end of the meeting. It is important to engage as fully as possible in these discussions as they are seen as a vital part of the relationship building process — coldness during these parts of the meeting could be very costly in both the short and long term.
Do not expect that everybody will have done lots of in-depth analytical planning for the meeting — they may have done but you can't be certain. Flexibility and spontaneity are both greatly prized in Argentina — as befits a country where people have traditionally been at the mercy of political and social forces beyond their control.
Punctuality is much tighter than in certain other South American countries but agendas are very likely to be ignored.