Vast majority of criminals are actually stupid though. For every criminal using quantum guaranteed encryption there will be 10 just doing normal unencrypted calls over regular GSM - you use the same tactics against criminals that have been used forever, before IMs were even invented - you infiltrate these groups, arrest lower members, get them to incriminate the people higher up until you dismantle the entire structure. Yeah I know it sounds simple and in reality there are million other steps to do this - but it has been done in the past and is still being done now. That's what the police will do. They caught criminals before they could read their messages, they will catch them again when they can't read their messages.