As Marilyn said, dongle is a NoGo.
Anyway, for the dongle you would need a SIM as well... Prepaid cards are available a lot over there..
Anyway, you should be aware that (except in the Region Metropolitana and outside major cities) reception is different for each carrier - I made good experience with EntelPCS. Also be advised that prepaid packets are charged by hour/ day/ 7day period and do have a restriction on data usage (even if the 7 days are not over, but the data usage exceeds the limit it will have to be re-charged)!
Restaurants, Bars and Cafe's however do offer free WiFi, you just have to ask for the password - that will be in any way the cheapest possibility to be connected.
BTW, don't forget the plug-adapter (2 round pin, Euro-style)
Personal question - where are you going to? (I have been living there for some years, just returned for a visit during vacations after 5 years back in Europe...)
