Here's my experience with Movistar and the internet:
I own a Nokia E72 unlocked USA version. When I arrived in BsAs I picked up a Movistar SIM and popped it in. Paid for $10 of credit and immediately gained internet access. Not sure why. Talked to a rep at the Movistar mothership on Santa Fe and she said that the SIM carded was "previously owned" by some guy named Eduardo. So maybe it's legacy access from Eduardo's contract? Whatever. The only thing I know for sure is that every app installed on my phone works perfectly - Opera 10, Skype, Gmail, internet radio, Google Maps, whatever. Yet whenever I recharge the phone it burns through every centavo of credit almost immediately, within minutes, no matter how much I pay. So now I don't recharge at all and use the phone strictly for the internet, receiving calls & texts, or Skyping other phones when necessary. About 10% of the time Movistar throws an error message saying that I need to recargame, but only when browsing the web, and never with Gmail or other non-HTTP protocols. Usually a few minutes later, or after I reboot the connection, everything returns to normal. In the meantime, I have a second, very cheap Movistar locked phone that I use when I need to make calls.
It's a bizarre system, no doubt, but you'll never find anything cheaper. I suggest you give it a try.