And No, not any US agency can request information from private telecoms without a warrant. Based on my understanding it seems likely that NSA can search when they please. The CIA, FBI, and armed forces probably can access for sensitive issues, but it may not be widespread. I highly doubt that smaller, less powerful or less interesting agencies get access to this information without a warrant. Just for the record I find this to be a gross abuse of our personal liberties and our right to be free from unnecessary search and seizure. It has to change and I think the best most practical thing we can do is email our representatives and express our rightful outrage. If you do not hear back or hear a defense of such searches follow up by promptly voting them out of office.