We have four unlocked phones in Brazil as I speak. Only one of them works properly. Our brand new iPhone X Plus, which was bought in the US but never opened and turned on until we got to Brazil and bought a SIM card, is working flawlessly. ALL of our other three unlocked phones that we have been using in the US do not work properly. They will receive and make calls but that is it. None of the apps work right. Whatsapp will not work, which is the major app we use to communicate with everyone. We also cannot access the internet, even though we have tried several different services, changed settings, etc. No matter which SIM we buy, our phones are not fully functional. Of course we are not buying very expensive "unlimited" plans. We are trying to buy 2 gig plans that are supposed to have unlimited calls, Facebook, and whatsapp. The iPhone X is working perfectly with one of these plans.
Our other three phones include a brand new LG V30, which we have only had for a week before we came to Brazil, an old Galaxy S3 which we have had forever and a iPhone 6s Plus which we have had for two years. All three are unlocked and accept Brazillian SIM cards. All of them will receive and make calls. None of them will connect to the internet. Three different carriers in Brazil have tried to change our settings but nothing has worked so far. We are so frustrated that we are going to go ahead and buy a cheap Brazilian phone to use while we are here. My wife is at the store as we speak.