• "Fitzgerald was appointed special counsel in December 2003 and began pursuing the case aggressively. The White House had turned over telephone logs, e-mails and memos to the FBI in October 2003, so Fitzgerald presumably had records of who had called whom. The prosecutor then demanded sworn testimony from a number of senior aides. According to the New York Times, the FBI interviewed Karl Rove and top vice presidential adviser Lewis "Scooter" Libby, and a grand jury heard testimony from press secretary Scott McClellan, Cheney aide Mary Matalin and others. Fitzgerald even conducted interviews with President Bush and Vice President Cheney....."Fitzgerald subpoenaed journalists to testify about their conversations with the possible leakers."
  Source: Washington Post

Telephone records and logs would show who talked to whom, but not necessarily the subject matter of the calls - and not everything that was discussed during the calls. For that, Fitzgerald would have questioned the officials.

Chicago Tribune, March 5, 2004:

In the grand jury sessions, press aides were confronted with internal White House documents, mainly e-mails and telephone logs, between White House aides and reporters and questioned about conversations with reporters, according to sources and reports.

The logs indicate that several White House officials talked to Novak shortly before the appearance of his July 14 column, the Washington Post reported. According to the New York Times, the set of documents that prosecutors repeatedly referred to in their meetings with White House aides are extensive notes compiled by I. Lewis Libby, Cheney's chief of staff and national security adviser.

The FBI has interviewed Rove, Libby, McClellan, Levine, Matalin, White House communications director Dan Bartlett, former White House spokesman Ari Fleischer and Cheney aide Cathie Martin, the Post reported.