Interface Arduino with iPhone/iTouch via 30 pin

First time on board, thanks for all the helpful resources thus far.

Simple question: Has anyone used an Arduino to communicate with an iPhone without using a computer a middleman?

I'm looking for a very low cost method of monitoring my engine performance via OBDII, as well as controlling a few hack job modifications i've done as practical jokes (water gun out the trunk, etc.)

As a newbie, i'm also looking for recommendations on which Arduino to invest in.

The Uno is new, but does it have enough pin inputs/outputs to control a few actuators, water pumps, as well as communicate with the OBDII port? Is the Mega a better route to go with?

Lastly, any experience out there in using xCode to create apps which communicate via 30 pin connector? Obviously, I am also attempting to keep my iTouch charged.

Many thanks in advance, Justin

Is using a multiplexer pretty simple? I suppose I'm curious what I loose by going with the Mega, or what I get by sticking with the Uno.