PHP - mbstring question

[Darryl Hoar]

Greetings,
I installed php4 and php4_extensions on my 6.3-release box.
Tried installing SugarCRM (downloaded from their site as the 
freebsd port is broken).   When installing it generates an error:

Functions associated with Multi-byte strings PHP extensions (mbstring)
are needed by application.

How do I add that ?   Any help greatly appreciated.

-Darryl

PHP version 4.4.7