Once upon a time, people mailed their holiday wishes to the North Pole and hoped for a reply on Christmas Day. Nowadays they are sending their wishes into cyberspace and are apt to get a reply in minutes.

America’s first Twitter Christmas got under way in earnest on Friday. Across the land, retailers and their customers used the social networking site to talk to one another about bargains, problems, purchases and shopping strategies.

After buying a new navigation system at 6 a.m. on the most frenzied shopping day of the year, Laura S. Kern of Los Angeles could not figure out why it was not giving her traffic updates. She sent a message to Best Buy’s Twitter account and within five minutes not one, but two Best Buy employees responded with fix-it advice.

In Bloomington, Minn., Mall of America used its Twitter page to tell consumers two of its parking areas were at capacity and that their best bet was to park near Ikea.