The technology to store all U.S. conversations on a hard drive I am not familiar with. That’s a question I could ask my Microsoft relative. However, the Utah NSA stores world wide data, including photos and videos from you cell phones and emails. That’s why we have intelligence satellites.
Rough estimate:
Sum of:
Average length of words spoken
# bytes needed for unique ID
# bytes for timestamp when when word is spoken
Multiplied by:
Population of US
avg length of words spoken
Avg number of words spoken per person per day
How many days you could fit on the hdd in your laptop?
How many hhds could you stack in your closet?
I did the math a few years ago.