If you're willing to jailbreak your Iphone, I believe this is possible. Take a look at this site which offers a perl 5.10.0 compiled and packaged for the Iphone 3G. It also requires you to have apt-get installed (
is that standard for Iphones these days? update: which apparently you get by installing Cydia) and a few other prerequisites, but it should be possible to get it running.
Also, I believe(I don't own an Iphone, never will), it should be possible to compile your own perl on a jailbroken Iphone. The author of the above packages gives some hints on how to compile apps on an Iphone here.