@vic
Uhhh ... 'This system is not registered to Red Hat Subscription Management.' Has your subscription for support expired?
Red Hat Enterprise Linux Server release 6.4 does have php-intl.
PHP 5.3.x may not be default for a RHEL server version 5.
What would you get if using:
yum list php53*
Also, you *MIGHT* be able to use CentOS repos:
http://cotdp.com/2012/07/installing-centos-packages-on-red-hat-enterprise-linux/
2 exceptions to the article above:
1. the repo URL might need to be pointed to a server closer to your location.
2. do NOT enable the repo by default: enable=0 in config.
Use by enabling the repo in the yum command itself for acquiring very specific software. Strongly advise study of yum if you mix CentOS repos with a commercial RHEL server.
'spirit of sharing', Ken