Well, sort of. This morning the PHP website announced that support for PHP4 will be reduced at the end of this year and discontinued completely on August 8th, 2008.
This announcement follows lengthy discussion on the internals mailing list regarding the best time to do this and what the likely impact will be. After much discussion a two-phased approach has been adopted.
Non-critical updates to PHP4 will cease at the end of this year. This basically means that no new development will be done and improvements to PHP5 that would make sense in PHP4 will not be backported from that date.
Then, from the start of 2008 to August 8th only critical (read "security-related") fixes will be made. All users are encouraged to make the switch to PHP5 as soon as possible. There are various migration guides available on the PHP website to help anyone moving from 4 to 5.
I think the most interesting reaction to observe will be that of the ISPs. A painfully large number of them don't yet support PHP5 and that will have to change. In addition there's a large number of projects out there that have not made the leap yet either.
As far as I'm concerned this announcement is long overdue. PHP 5 has been out now for 3 years and over that period it's become as fast and as stable as PHP4 is/was. There's little technical reason I can see to stick with PHP4, and this timetable should encourage individuals and organisations to make the switch sooner rather than later, which I think is the intention of the announcement.