Now somebody here claims it's around 1e7 B compressed for an hour of phone talk (not transcribed only compressed). That gives 2e10 hours stored. Storing it for 2e8 Americans there's space for 100 hours per person. But they also want the world, not only Americans.
Even if, as you say, the estimate is 100hours per person. How much time does the average person spend on the phone? My current cell plan has 200 minutes per month, and I never go over. Say the average person spends 1000 minutes (16.7 hours), that means you could store a month of rolling phone conversations, and be only at 16.7% capacity. That leaves a fair bit of extra room for persons of interest internationally.
Regarding my estimates, somebody here on HN also sent a link to the highest capacity automated tape libraries, and using them instead of hard disks the estimation of capacity still fits in the same order of magnitude. I still assume hard disks are more convenient than tapes for anything that needs to be accessed "when needed" (who would accept to say "will get the data bout the terrorists regarding the attack tomorrow, but it will take two days." So I can even bet that the main storage there are hard disks.