I could be wrong, but that Reuters article seems to be saying that the White House was not actually "eavesdropping," on, or monitoring the content of, any of those calls.

Instead, the article seems to say, all the White House did was obtain information directly from the telephone company regarding calling patterns and the like: "who is calling whom, how long a phone call lasts and what time of day it is made, as well as the origins and destinations of phone calls and e-mail messages."

Furthermore, the article seems to state that the phone companies were already maintaining these records and turned this information over voluntarily.