[sgxin]

Ok, let's see how Huawei manages to squeeze an efficient antenna operating in the satellite band into their handphone. As it is with their existing phones, there is already very limited estate for such antennas and given that you need higher efficiency when communicating with satellites, it remains to be seen how such an endeavor will bear fruit.

It is SMS via Beidou and not Satcomm voice comm. 
All existing phones already have built-in antenna to receive either GPS or Beidou signals so it will likely just be an enlarged version of the embedded antenna.
Also the short SMS transmission (uplink) should be be in high powered pulses that the low orbit satellites can pick up, somewhat similar to radar signals where the peak signal strength in radar pulses can be 1000 times that of the input power.

iPhone 13 is rumoured to have satellite-based SMS too according to this video: