Pecl will only try to install PHP extensions in /usr. But OS X's security model prevents that. This work-around works around the problem and installs extensions in different spot. This example is for intl, but this method should work for any extension.
pecl download intl tar -xzf intl-3.0.0.tgz cd intl-3.0.0/intl-3.0.0/ phpize ./configure --with-icu-dir=/usr/local/opt/icu4c make -j4 make -j4 test cp modules/intl.so /usr/local/lib/blah/blah/blah/no-debug-non-zts-20121212/intl.soMangle /etc/php.ini and add
extension=/usr/local/lib/blah/blah/blah/no-debug-non-zts-20121212/intl.soRestart apache and intl's your uncle.