When to buy unlocked phone

I don't know about the other countries, but you are better off buying an unlocked phone in the U.S. instead of Buenos AIres. You will get a better phone for the money, especially if you get a used one from eBay or Craigslist. Plus many of the used phones for sale in BsAs are stolen phones. You can buy a cheap feature phone, but if you want GPS and apps, those handsets will be pricey.

You don't mention what type of phone you want, but I have a Nokia Lumia 620 Windows 8 phone with Nokia maps that works very well without data in BsAs.

However on prepaid phone plans (Movistar or Personal), data (probably 2G) is very cheap, but it is slow. There is a lot of free WiFi in BsAs.

If you get a US unlocked phone, make sure it is quad band. If not it will not work anywhere else in the world.

A phone in BsAs are more sure to be fully unlocked and globally GSM.

You can get a new phone for less that 20USD -- I use a Nokia 1280. good battery life; black and white screen; flashlight. Works everywhere -- except the US and Japan. Chinese phones are even cheaper.

In Mah Boon Krong (mall, Bangkok, Thailand) on the 4th floor, there are plenty of phones for sale, and plenty of people who will unlock phones for you.

I agree with #1, get an unlocked, quad-band, GSM phone off Ebay or Craig's List. Lots of good phones with all the features you want at reasonable prices.