QUOTE(JLA @ Jun 13 2020, 12:35 PM)
did you know many 4G smartphone second sim is 2G only ? Can we call dumb smartphone

Older models of 4G smartphones with dual-SIM (usually those before 2015 model ones), it is true that the second SIM supports up to 2G only.
But certain 2016 models onward ones, the second SIM slot can support up to 3G, while primary SIM slot is 4G as usual.
However, most of the recent years model ones, can support dual 4G mode (both SIM 1 and SIM 2 slots can connect to 4G at the same time), and some even dual VoLTE as well.
One of the examples are Samsung Galaxy S9/S9+ onwards, Huawei P20 Pro onwards....
So it really depends on the phone model.
But yea, if 2G network is shut down in the future, and your phone's second SIM slot supports up to 2G only, then basically your second SIM slot becomes useless already.
It's like, dual SIM phone but can only use 1 SIM card (up to 4G).