Let me first start by saying I am not taking sides on this issue, I simply want to shed some light on facts surrounding it.
Currently the NSA is collecting call meta-data. Meta-data include the originating phone number ESN (serial number), date/time, GPS coordinates when the call was placed, the duration, and the call and the destination phone number. Meta-data does NOT include personally identifiable information. In fact, The Supreme Court has ruled in the past that meta-data is not personally identifiable, and therefore a warrant/subpoena is not required. If the NSA wants personal information they must submit a warrant to the carrier, which still requires probable cause.
Now then, lets talk about how this data is currently used. Lets day, hypothetically, that a bad person was planning committing an attack on US soil, and they are arrested. While being arrested the govt. finds that they have a cell phone on them. They take that device and cross reference the MDN and/or ESN with the list and determine that they talk to two other daily, and that they spoke to them as little as 10 minutes before the attack was planned. The govt. could then take the meta-data in conjunction with a warrant and determine who the suspect talks to regularly, and who they network with.
It should be noted that this has been happening for years, and with all major carriers. The carrier must comply with the order.
Perspective: Most everyone here voluntarily gives up tons more information to Bing/Google voluntarily than the govt. could ever collect. Specifically, Google know what your favorite foods are, what kind of movies you like, your physical location, what kind of browser you use, what your hobbies are, even what kind of porn you fancy. Google, for example sets a cookie that typically doesn't expire for at least 2 years (I have seen upwards of 12 years). This cookie also has a traceable GUID that is used to trace you online.
Hope this helps!