The link you provided specifically says the device doesn't support the iPhone - see the chart at the bottom of the page. Other similar devices only seem to support the iPhone when it's in 'Flight' mode.
More expensive ones
such as this do seem to support iPhones, but it'd be worth checking whether this is only up to the iPhone 4/4S generation, or whether they'll work with the new phone with the Lightning connection, or indeed with the phone with a Lightning adapter.
This one, for example, does say specifically that it will work with, and charge the iPhone 5 via a Lightning adapter.
Assuming that's sorted, there's a number of YouTube vids covering such installations - looks pretty simple to me, in that it's a matter of pulling the head-unit, swapping a couple of plugs and then putting it all back together.