When I initially charged my phone and bought a 10 pesos/2GB/2day data plan, another 1/2 pesos mysteriously disappeared from my account, even though I did no texting or voice calling. So I as forced to buy another card just to get enough to buy another plan 2 days later. Also, I got a promotion one day and received double the credit but somehow most of the extra credit mysteriously disappeared the next day even though I made sure I turned the phone into airplane mode before the data ran out.

I found movistar about 75% reliable in Buenos Aires (and 100% reliable in Puerto Iguazu). Often I would get 5 bars showing and movistar 3G showing but could not use the data and then mysteriously an hour later it would work again. Resetting the network settings didn't seem to help. Also, to save battery power I put my phone into airplane mode and turned on WiFi in restaurants and coffee shops (where WiFi seems to be ubiquitous) and only took it off airplane mode when I wanted to use the phone. I found myself surfing and using Google Maps quite a bit and using Skype the odd time over 3G/Wifi to make the odd call here and there. Unlike some reports I've heard I saw many people flashing around their phones on the street as they made calls, but I kept mine pretty hidden as I hear it is a target of thieves and muggers.