This extension may be installed using the bundled version as of PHP 5.3.0, or as a PECL extension as of PHP 5.2.0. In other words, there are two methods to install the intl extension.
Information for installing this PECL extension may be found in the manual chapter titled Installation of PECL extensions. Additional information such as new releases, downloads, source files, maintainer information, and a CHANGELOG, can be located here: » http://pecl.php.net/package/intl.
Alternatively, --enable-intl will enable the bundled version while compiling PHP.
If your ICU is installed to a non-standard directory then you might want to specify its location in LD_LIBRARY_PATH environment variable so that dynamic linker can find it:
Otherwise, if PHP and ICU are installed to their default locations, then the additional options to `configure' are not needed.