Why would the NSA not be able to store all phone calls as audio? If we assume 30 minutes per person per day to store at compressed 20kbps at $0.12 per gigabyte

Why would the NSA not be able to store all phone calls as audio? If we assume 30 minutes per person per day to store at compressed 20kbps at $0.12 per gigabyte per year (this is what you pay at Amazon), that costs $60 million to store for the data of a year's worth of phone calls of the entire population of the US. The budget of the NSA is more than $10 billion, so that's less than 0.6% of its budget. That is entirely doable. Note that I have grossly overestimated the cost here by assuming that price per gigabyteyear is what you pay Amazon, and 30 minutes per person per day is probably an overestimate, and the compression could be better too. The actual cost is probably closer to $10 million; less than one thousandth of the NSA's budget.