You can use 4g sim in 4g/3g/even 2g phone. … offcourse you can use it, they are making all customer to use 4g simcard for better network reception. Airtel 4G simcard can be used in any mobile , we can use 2g, 3g, 4g(if compatible) not like JIO. it is very easy 1 min work, go to any airtel store with number.