The flood of inquiries, which at times led to long queues of calls at the switchboard, is in response to a mailing of 11 million letters to members giving individual details of bonus entitlements and checking account records.
A Halifax spokeswoman denied reports that the calls were from furious customers who have been told wrongly they are not eligible for share bonuses averaging pounds 1,000 a head.
"Whether they are furious is another matter. We have had a lot of basic inquiries seeking reassurances or more information, or volunteering further information," she added.
Halifax was aware that there might be some discrepancies in the account details mailed to customers and "we want to be sure our understanding is the same as their's".
For example, some callers had several accounts opened in different years, and the details of the address on one of the accounts - such as a house name - might differ.
The computer would read this as belonging to a separate member and the mailing was to allow such discrepancies to be eliminated.
"With more than 11 million going out, to have 400,000 telephone calls is not a huge proportion," said Halifax.
One common complaint appears to be that the information in Halifax documents on how much must be retained in an account to qualify for the bonus shares is not clear.
"I was on the phone to the Halifax for 20 minutes trying to get this sorted out," an angry caller told The Independent.
Meanwhile, Halifax said it was appointing Gren Folwell, former head of the building society and estate agency subsidiary, as deputy chief executive. James Crosby is to be financial services and insurance director, Mike Ellis is to head banking and savings and John Lee will run personnel and services.