You say this as if it's an easy thing anybody might do -- like putting flowers in a vase in the kitchen. Isn't it pretty complicated?

I cant speak to 2G networks, but 5G (and 4G) are amazingly simple to get started using OpenAirInterface. With a USRP B210 I had a 5G network running from a bare Ubuntu install in under 30 minutes. I used a smartphone and some cheap (blank, user-writable) SIM cards to connect and test it.