Hi, MadamCandy The_Chief answered and explained it very nicely. I would just like to add 1 point or rather say elaborate. You cannot chat if you don't have an active internet connection or consumed 100% of your mobile data. But you can send a text SMS from your message app all you need is an active cellular connection. People don't use the basic cell phone that much, nowadays, that had no net connection just a dial pad and a small screen. Like the prepaid phones in the USA. Vice versa you can chat if you have an active Wi-Fi Internet even if your cellular service is not active or there is no signal.