Coming down with Iphones and selling them here is possible, but please note its not a walk in the park. There are a very good number of businesses that do this already so you will face stiff competition... plus if you list the phones on Mercado Libre the fact that you don't have a track record and proper reputation will also affect your chances of making quick sales.... also, to sell them as new/unused, you MUST have all original packaging and this means the transparent plastic foil/film needs to be unopened, else the market price for the phones goes down. You may also need to deal with logistics and delivery as buyers may want you to send things by mail and this adds more work, etc.

While you can sell for cash, you will have to do this with folks that you don't know and there are risks/pitfalls you need to factor in. You also must offer the Mercado Pago payment option that Mercado Libre works with so this may mean that you do need some form of local banking (not 100% sure on this, you must read the fine print when you sign up for an account). I don't mean to burst any bubbles but there are issues you have to deal with... also, you will need to be quite proficient in Spanish (read/write).