On the SitePoint PHP blog, there's a quick tutorial from Troels Knak-Nielsen about the creation and use of dynamic global functions in your PHP application:

Like many others, I prefer to use procedural PHP as a template language. While PHP's syntax makes it a practical choice for this, there is a problem with embedding dynamic content. [...] A single letter, regular function is undoubtedly the simplest way to extend PHP's syntax. Thinking about it, it's fairly obvious, but it just never occurred to me. [...] There is a problem though; Since this is such a good name for a function, chances are that someone else would use it for something different, or perhaps even for the same.

As a more viable solution, he recommends going dynamic and creating fumctions (via the call_user_func_* functions) and an addition to the $GLOBALS superglobal to make calling the custom function simpler.