Use UConverter class on PHP 5.3

Use UConverter class on PHP 5.3

I have PHP 5.3.1 installed on my system (Ubuntu 12) with intl extension
installed with apt-get install php5-intl. While I'm able to use such intl
classes as Collator and Locale, I can't seem to use other classes like
UConverter:
echo UConverter::UTF16;
outputs
Fatal error: Class 'UConverter' not found in ...
Do I need to upgrade intl extension to the latest version? Would I
preferably be able to do so while keeping PHP at the current version?