I didn't test it on FreeBSD, but some peple report what it work fine on OpenBSD. So I think. it should work fine on FreeBSD too.
I'm using it on FreeBSD without any problems, just make sure you install mm for the shared memory (this has to be installed on Linux as well so it is not a FreeBSD specific requirement).
I'm using Apache 1.3.27, PHP 4.3.1 on FreeBSD 4.7-STABLE.