Facebook fans hungry for an @facebook.com address, get ready.

The much ballyhooed Messages, where e-mail, text messages and are linked in a "social inbox," will be offered to a majority of the more than 500 million Facebook users over the next two months.

"The reason we're taking our time with it is we're not starting from scratch. We're starting from being one of the top messaging systems on the Internet," said Andrew Bosworth, the Facebook engineer who lead the team that, with extensive input from Facebook CEO , developed the new Messages product. "This is a new product with 500 million existing users."

Messages was launched in November, amid media buzz that it would be a "Gmail killer" that would render traditional e-mail obsolete. Initially, however, Facebook gave relatively few people access to the new product. Over the past two months, the Palo Alto company has been painstakingly moving existing content over to the new service, a transition that will ultimately encompass more than 100 terabytes of data - or about half the total digital archive held by the Library of Congress. Bosworth said Facebook software has been checking every character within every message, scanning for discrepancies as each user is switched over to the new service, and assigning an engineer to manually check every error it discovers.

"We have billions of messages in the existing system that we have to move over to the new system," he said. "These are intensely meaningful, personal messages that people expect to have access to, and we have to do this with some care."

The new service treats every communication between people as part of an ongoing conversation that began with their first interaction on Facebook - a string that in many cases goes back for years.

"Facebook is not just about what's happening right now, it's also the history of what we've done before," said Bosworth, a native of Saratoga.

The system is intended to allow people to carry on a single conversation over a variety of devices, perhaps starting an interaction on e-mail through their office desktop computer, then moving to on their phone as they head outside, or moving into Instant Message as they come back to their office PC.

Zuckerberg took a direct role in the shaping of the new Messages product, starting with a series of conversations with a group of teenagers during a Thanksgiving break in 2009, where the younger people told the Facebook CEO that they favored text messages because e-mail is "too slow." "That was the catalyst," Bosworth said, and his team held extended weekly meetings with Zuckerberg through the spring of 2010 as they built prototypes of the new service.

The night before the service launched in November, Zuckerberg even camped out with the Messages team, working through last second bugs.

"Zuck, most of all, realized that the thing we were trying to do is connect people across media and devices and make it really easy and simple to talk to a person," said Bosworth, who has known Zuckerberg since he was the Facebook CEO's teaching assistant at Harvard.

Messages has not been universally well received by analysts, who say it is not functional enough for business and other uses. Matt Cain, an analyst who follows e-mail trends for the research firm Gartner, believes Facebook is working on a new version of Messages that would incorporate many of the features of Google's Gmail, Yahoo Mail and Microsoft's Hotmail, such as subject and cc: and bcc: lines.

Cain said that because e-mail remains such a big source of time spent online, and Facebook wants people to spend more time on its network, a more functional e-mail service is a business imperative.

"It would be at truly bad business decision on the part of Facebook not to aggressively go into the full-blown e-mail market, because they can immediately capture a very substantial chunk of the consumer e-mail population," Cain said. "There are tremendous monetizing opportunities."

Other than saying Facebook is "always working on ways to improve the system and make it so people can send messages faster" a spokeswoman declined to comment on whether it is working on another generation of Messages with more features. But Facebook has begun offering Messages to users outside the United States, and over the next month, an increasing number of users in all countries will be offered the new service.

"Over the holidays things were moving a little slower. We wanted to make sure we were taking the appropriate care migrating those messages over," Bosworth said. But now, "we're really starting to move on the invites."