Hi,
But I can upgrade my server from php4 to php5 AND php4 with easyapahe 3?? This is a best solution? for my customers with use php4?
The vast majority of PHP 4 scripts will work in PHP 5. From experience, most distributed scripts that don't work in PHP 5 are very outdated and thus could pose a security risk to the server.
However, supporting PHP 4 and 5 simultaneously is a great way to transition your customers to PHP 5. If for some reason a website malfunctions in PHP 5, they can still use PHP 4 temporarily until they can take corrective action to migrate to PHP 5.
It is important to note that PHP 4 is EOL (as of 8/8/8) and thus is no longer receiving security patches. PHP has a history of having security issues, so it is best to migrate your users to PHP 5 as soon as you can to mitigate the risk presented by running an EOL'd version of PHP on a production server.