It is. Denmark is allowing the phone companies to use their existing 2G/3G and 4G frequencies for 5G. The 700MHz spectrum is also being opened up for use with 5G.

I'm not sure if it will result in dramatically more bandwidth though.

If it is possible, and those frequencies are worth using for this purpose, maybe they should give free 4G/5G-phones to anyone still on 3G to be able to do it as soon as possible.