Well, last December we heard the NSA was tapping the phone conversations of people some of those taps were of conversations between people in America and those outside. The key point of outrage s the in America portion.
Now, it is revealed the NSA was being given phone call records by quite a few of the phone network companies. Of course the usual suspects are outraged by this.
The two reports have the appearance of separate programs. However, it seems the latest revelation is an early step in the whole program. After all, the NSA is not going to be able to tap every single phone conversation (let alone analyze for interest then reanalyze those that warrant interest). The NSA has to have a way to detect numbers worthy of further scrutiny.
This is what we are seeing now. If a given phone number makes repeated calls to Kandahar Afghanistan, Waziristan Pakistan (or to known terrorists) or similar, then the government has good reason to escalate their interest in both ends of the conversation. I would guess further analysis of both numbers is conducted and sooner or later it reaches the tapping stage, which one (IMO) may reasonably conclude is not the last level of scrutiny.
The constitutionality of the program? I subscribe to the view the executive is assigned by the constitution to the protection of the homeland and the prosecution of wars. Those making war upon the USA fall outside of constitutional protections. This applies to citizens as well as non-citizens.
Furthermore, little, if any privacy is compromised by this sort of traffic analysis. It is the filter by which probably tens of thousands of numbers are selected for further scrutiny.