can use my 3G simcard on my 4G phone? Would that work?
The 3G SIM will give you access to the 3G & 2G spectrum available in your network, but you will need a higher capacity 128kB 4G nano/micro SIM to access 4G data speeds on your 4GLTE enabled phone.
Once I got my Airtel 4G sim, I continued using the 3G SIM till I got an sms confirmind 4G SIM activation from Airtel when I switched off phone and changed SIMs. Upon switching on phone I had access to blazingly fast 4G LTE speeds.