Whilst talking about the PlayStation Plus (PSN+) service, Sony added to the end of their press release that:

“PlayStation users can purchase PlayStation Plus membership through PlayStation Store on PS3 only. Users need to install PS3 system software version 3.40, which will be released on June 22nd, to enjoy PlayStation Plus,” revealed the press release.”

So there is the confirmation that firmware version 3.40 will be available to download to PS3’s in the next few days to be ready to join the PSN+ revolution which itself launches on the 29th of June.