How much does it cost to ship an iPhone 4 to Argentina?

Sold my iphone 4 on ebay but the buyer is in argentina

Easy, use the post office. First, send an invoice and get paid. Use USPS to calculate the freight.

Then after you have been paid. Go to this site, chose a method, surface mail is cheaper than air mail. Pack, weigh and measure your package. Using this site, pay by credit card, fill in the combined mailing and customs form and print them from your computer, stick the label on the package and drop it in the nearest mailbox.

Note, put the item as "Free gift", then the recipient may not have to pay duty.

Done.

https://www.usps.com/

My rough estimate: Surface mail, six weeks, $ 12.00 Air mail, five days, $ 19.00. Your package is insured against loss up to $ 100, you can pay for more. Nobody can insure you against breakage, pack it well.

I'm going to guess at least $20. You should have had eBay calculate the cost before you offered the item so you know how much to charge. It all goes by air, there's no cheap alternative.