It's very likely a ton of people, but it's also very likely nearly impossible to measure.
If you're the CIA and you're tracking the cell phones of say 10,000 foreign suspects for 10 years, and each of those phones is making 10 calls/week, you're at 50 million calls to analyze. You could probably look at the country code to get an estimate, but if the other side of the call is a foreign national in the US, they shouldn't count. If the non-US country codes happen to be owned by US citizens who may be traveling, how would you know?
Phones at least have country codes.. How in the world can you assign a country of origin to random email data or plaintext data through a router somewhere?
If you're the CIA and you're tracking the cell phones of say 10,000 foreign suspects for 10 years, and each of those phones is making 10 calls/week, you're at 50 million calls to analyze. You could probably look at the country code to get an estimate, but if the other side of the call is a foreign national in the US, they shouldn't count. If the non-US country codes happen to be owned by US citizens who may be traveling, how would you know?
Phones at least have country codes.. How in the world can you assign a country of origin to random email data or plaintext data through a router somewhere?