Washington Mutual (WaMu) was about the only bank in the US that didn't charge ATM fees, but they discontinued that practice a couple years ago. Afraid you are probably out of luck in the US regarding free ATM access fees. I use an internet bank in the US that doesn't have its own ATM system - they reimburse me for up to $6.00 in ATM fees each month and as a consequence between that and using WaMu I haven't paid ANY bank service fees in years (when in the US). Canada has its own banks, weren't to unreasonable for the couple weeks I used Canuck ATM's.
I travelled through Cent. Am. in 4th quarter '06 - and am presently in Ecuador after having been in Colombia. Can't speak for the rest of SA.
As to Central and South America, there isn't a 'south american bank' - there's about 18 countries and I don't recall seeing any international banks serving them. Maybe there's a few International banks with branches in major cities in some countries, but I never investigated that - never saw them where I travelled. I just used each countries local bank. For the most part, I only paid currency conversion charges using my Visa debit card - generally in the neighborhood of 50 cents (USD) per $100. I occasionally paid an ATM charge - generally $1.50 USD, but it was rare - and I didn't shop around, just used the first ATM I found that was on the Plus system. (some places, there ain't any shopping around to do - there's an ATM, you use it).
Just guessing, I don't believe I have paid more than $10 USD per month for ATM fees and/or currency conversion charges since hitting Mexico in September - usually less than that I'm guessing (my charges are low - don't add them up at the end of the month). Maybe it has something to do with US bank issued Visa cards - could also be because El Salvador, Costa Rica, Panama and Ecuador recognize USD as official currency so I didn't have to pay currency conversion fees. Also, I take out $200 to $400 at a crack to minimize ATM fees.
Maybe the thing to do to hold down fees is to try to set up a Checking Account with a U.S. bank, get a Debit card attached to it and use that in N & S America - keep pumping money into the account from your main bank.
Chiang Mai, Thailand