I see though:
# rpm -ql php53-common-5.3.3-1.el5 | grep modules /usr/lib/php/modules /usr/lib/php/modules/curl.so /usr/lib/php/modules/fileinfo.so /usr/lib/php/modules/json.so /usr/lib/php/modules/phar.so /usr/lib/php/modules/zip.so
So json and fileinfo are probably built-in now?
Sorry, I'm not very proficient in PHP (and many other things :-)
Regards Alex