SAN FRANCISCO — Just as it transformed online social relationships, Facebook is now hoping to reshape how people communicate on the Web.

The Palo Alto social networking giant on Monday announced a new service intended to unify e-mail, instant messaging, text messaging and its existing message system in a “social inbox,” aiming to become a hub for all its users’ online communications.

While the social network’s more than 500 million users will have the chance to get an @facebook.com e-mail address as the new service gradually rolls out in coming months, CEO Mark Zuckerberg said the goal was not to create the world’s largest e-mail network, but to launch something that would stress what people say rather than how they say it. Facebook, he said, hopes to breach the walls between e-mail, text messages and instant messages.

“This is not an e-mail killer,” Zuckerberg added in remarks to journalists at a heavily attended announcement in San Francisco, where the tech media is massed this week for the Web 2.0 Summit. “This is a messaging system that includes e-mail as one part of it. We don’t expect anyone to wake up tomorrow and say, ‘I’m going to shut down my Yahoo Mail or Gmail account, and switch to Facebook.’ “

The Facebook messaging system, in fact, is less functional than many existing e-mail services, lacking features such as a subject line, CC: or BCC: buttons, or even a send button. Because of those limitations, some experts said they were underwhelmed.

“Maybe I got caught up in all the hoopla, but I was very uninspired by what they actually announced,” said Matt Cain, a senior analyst who follows e-mail technology for the research firm Gartner. “I think our friends over at Google and Microsoft and Yahoo and AOL, they are all breathing a sigh of relief today.”

Transformative?

But other experts argued that Zuckerberg’s vision — Facebook engineers said the system that emerged Monday was very similar to what the CEO envisioned when he sat down with them 15 months ago to begin what was dubbed “Project Titan” — could end up being transformative.

“Comparing it strictly as an e-mail system is the wrong way to view it,” said Augie Ray, an analyst who follows social media for the research firm Forrester. “I think Facebook is really seeking to change the nature of personal communication. As with everything Facebook is doing, it’s really about facilitating the real-life relationships and friendships you have in the real world.”

“I think younger consumers will adopt this really quickly, because this is in many respects similar to their favorite forms of communication,” like text messaging, Ray added.

Zuckerberg, 26, said his vision for the new system evolved partly from his conversations with high school students, conversations that “make me feel really old.”

The new system will allow Facebook members to send e-mail from within their Facebook page to any Internet e-mail address. But it also will allow users to see incoming e-mail on their Facebook page, or a text message sent to their phone.

The system will also create an archive of ongoing conversations with individuals, meaning that a Facebook user could see all communications with that person, whether an e-mail, text message or chat, by going to a single place on their Facebook page.

It knows your friends

And Zuckerberg said that because Facebook knows its users’ networks of friends, it would be much more efficient at filtering out spam or less-important e-mail messages.

Facebook plans to display advertising with the messaging service, although unlike Gmail, Zuckerberg said the ads will not be targeted by the keywords in the message.

While AOL rushed out a new version of its e-mail service over the weekend, competitors like Google and Yahoo said they were unconcerned about Facebook’s move.

“More competition is always good, because the competition makes the market larger,” Google CEO Eric Schmidt told journalists at the Web 2.0 Summit, where he showed off a soon-to-be-released version of the Android smartphone operating system that will include an embedded payment chip that will allow people to use their smartphones like a credit card to make purchases.

The newest version of Yahoo Mail, meanwhile, already allows people to send text messages and instant messages, as well as archive content, from their e-mail inbox.

Andrew Bosworth, the Facebook engineer who headed “Project Titan,” said Facebook’s main thrust was to allow people to focus on the conversation rather than the channel, not to eclipse existing e-mail networks.

“The goal for us is to make it easier for people to connect with the people they care about,” he said. “If they find it easier to do that through Facebook, cool.”

Contact Mike Swift at 408-271-3648. Follow him at Twitter.com/swiftstories.