My question is: how many networks like this are across the country, from the large urban cities to the small rural towns?

https://www.nbcnews.com/politics/national-security/secret-service-agents-dismantle-system-used-convey-assassination-threa-rcna233115
In five locations within 35 miles of New York, Secret Service agents discovered more than 300 co-located SIM servers and 100,000 SIM cards, officials said. They said the system could also be used for criminal activity and that 80 grams of cocaine, illegal firearms, computers and cellphones were also found.
"These devices allowed anonymous, encrypted communications between potential threat actors and criminal enterprises, enabling criminal organizations to operate undetected," Matt McCool, the head of the Secret Service New York field office, said in a video statement released Tuesday morning. "This network had the potential to disable cellphone towers and essentially shut down the cellular network in New York City."