I ported from Vodafone to Airtel, now in my airtel sim volte enable option is not available. but when I inserted another airtel sim into my mobile then volte working properly. And my same airtel sim card insert into another phone then also volte working properly. I reset my phone totally (lost total data), than VoLTE is working fine, but i lost sim and than get a new Airtel sim than again VoLTE is not coming. I tried with *#*#4636#*#* but there is no VoLTE enabled option. Build number 2007.084 My phone is Asus max pro m1.