I assume that the cost and complexity of doing analysis on the millions (billions?) of phone calls daily limits even the government to metadata analysis, from which they likely issue orders for the contents of specific conversations based on statistical anomalies that may indicate whatever they're looking for.
Recording all US telephone calls costs only 2 million dollars for hard drives per year. Of course plus bandwidth costs, electricity and so on, but it is far less than at least I would have expect. Analyzing all the calls is of course a whole different story but I am not convinced it is not feasible or will become feasible in a not to distant future.
