Re: A technological Solution
"That's not very likely beyond monitoring every call for some sort of key word,"
No need. the metadata would give it away.
ie: Lots of short calls to one particular set of numbers.... Geolocate those numbers and the associated web of calls and you have your connections.
As many others have said, the drug "problem" isn't a policing problem anyway. It's a health problem and best fixed by addressing the issues that cause people to start using (most "addicts" use drugs to get a respite from a shitty life and stop using if life improves - something that the Rat Park experiments support (there's a real addiction rate of less than 2% and that's lower than alcoholism - treatable too))
The gang problems are best solved by taking the part away that the gangs are really about - MONEY, and again that's a public health issue - as Switzerland and Portugal have both proven. When we stop "blaming" and punishing the poor for being poor (a particularly anglo-saxon/Calvinist/fundamentalist prediliction) then things change for the better.
I'm not advocating drug use, but by taking away the gangs customers and insane profit margins (a medical knockout dose of cocaine or heroin is worth well under 50p, with a street value upwards of 50 quid - meaning there's always someone willing to take on the risk of selling for the reward), you won't get highly profitable materials being pushed towards "new customers" (ie selling crack to schoolkids). You don't take the customers away by punishing them - that just makes things worse. This is showing in Portugal where the narcogangs have almost given up.