Even before whistle blowing hero Edward Snowden revealed the deep penetration the US government has impinged on it’s citizens privacy as you use the internet, there were many reports of government institutions spying on citizens, and cellphone records have often been mentioned in those reports. In spite of this, we have as a whole ‘learned’ to accept it.
Cell phone use records offer tremendous insight into any investigation, because of the sheer amount of detailed information about the individual suddenly under the microscope.
Apart from basic contractual information like a subscriber’s name and address, lots of other data is also gathered and stored on file by mobile providers; such as everywhere you have been with your phone.
This database of data includes who you phoned (and they have the same type of data warehoused on your friends too of course), who you received calls from, who you sms’d, what you said, who said what to you, your tweets and facebook activity, your photographs are up for grabs, videos, and again, everywhere you have been.
There is not much left, as the above is already above most people’s imaginations.