As of today (mentioned in this post on PHP.net) the PHP4 life cycle is finally coming to a close:

Today it is exactly three years ago since PHP 5 has been released. In those three years it has seen many improvements over PHP 4. PHP 5 is fast, stable & production-ready and as PHP 6 is on the way, PHP 4 will be discontinued.

The PHP development team hereby announces that support for PHP 4 will continue until the end of this year only. After 2007-12-31 there will be no more releases of PHP 4.4. We will continue to make critical security fixes available on a case-by-case basis until 2008-08-08. Please use the rest of this year to make your application suitable to run on PHP 5.

They link to a migration guide for users moving up from PHP4 to PHP5 including guides for the PHP 5.0 to 5.1 switch and the PHP 5.1 to 5.2 switch.

Community Posts:

• Derick Rethans
• Clay Loveless
• Antony Dovgal
• Nick Halstead
• comments on the php|architect site
• Lukas Smith
• Gregory Szorc
• Marco Tabini
• Vidyut Luther
• PHPEverywhere