One of the biggest problems facing PHP web hosting companies is the big move to PHP5 that that end-of-life announcement. Arnold Daniels has one idea for a solution to help ease the problems - providing customers with a testing environment they can try out their code in.
A few months ago I've posted an article about running multiple Apache instances with different PHP versions. In that article I showed how to make multiple configurations running Apache on different IP addresses. By using different ports instead of different IP addresses, we can give our customers a way to check their site before it goes live.
He modifies the settings in that tutorial with a few updates he includes to make two different apache configurations - one for PHP4 and the other for PHP5. When used together, they can run two different PHP versions on the same code, just on different ports.