Look at the top right coner just left of the battery. I don't why, but when I get 2 bars of single then it stays 4G. It doesn't go to 3G or 2G. If someone know about this or get confused by this. I don't know if its a problem or if its normal. But I had the Samsung Galaxy A10s for more then a month. Sometimes I get 3 bars of single and 2bars of single.
