Unfortunately I don't know what options are available for REST. What I have found has just been through various blog posts and the little big of documentation that's included with the source. You might just have to go spelunking around in the actual source code to find out what's available (assuming you can read Java
)
I don't write in PHP either, but a quick search for perl ics on Google actually turned up this Apple web page which talks about parsing .ics files using both Perl and PHP:
iCalendar Files on Mac OS X