SCEE's just confirmed that there will be no in-game messaging included in version 2.20 of PS3's firmware, just announced and to be released before the end of March.
"No," a rep told videogaming247 when asked if the functionality would make the update. "Otherwise it would have been included in the press release."
You can take it as read, then, that in-game XMB access is also off the menu for now.
The big news for the firmware upgrade is the inclusion of BD-LIVE options, which allow users to access extra content and features through Blu-Ray movies.
System updates include the ability to play DivX and WMV files over 2Gb and a "resume play" feature that plays Blu-rays and DVDs at the point they were stopped, even after the disc has been removed.