Everything! The first thing is they don't do a one only upgraded nor will they replace a phone that has a cracked screen even though there are technically defaults: Overheats, freezes kicks you out of apps or researching. But the number one thing is connecting to your family who has iPhones. I can message on google messaging and Messenger. However, I can not receive their messages or phone calls unless it's on Messenger. They say their carrier is T-mobile however while I was researching on why I found where T-Mobile does allow iMesaging where assurance doesn't. It has been a real problem between my family, care provider, and Drs and I.