I think there's a lot more tapping of cell phones than we realize. They're not super secure, and it's a way to monitor activity. That being said, I think we deserve some privacy when it comes to cell use and police shouldn't monitor cell usage without probable cause and without getting warrants.
Technology has gotten to the point where it rules every aspect of our daily lives. So much so that we have forgotten how to protect ourselves. It is not hard for the police or any other government agency to tap into our phones and see our private information. The Patriot Act has made this so much easier to do so be careful what you say on a phone.
Not only do I believe this, I know it for a fact. I have met police officers that have admitted to doing this despite the fact that it is not quite legal. I have no doubt that as long as technology exists, people will use it however they can get away with it.
It has been reported that there was a 2011 secret agreement between the Department of Justice and the Baltimore police commissioner to tap cellphones. There is every reason to believe that this same agreement was made between other large city police departments and DOJ to tap cellphones in their jurisdictions, too.