I'm interested in iphone app with posibility of make the envoirment with the same app without use PC.The easy form is make an app with buttons options and in the button write manually the comand for send "GET" or other commands for example: http://192.168.10.254/?cmd=C (i use this simple config for send commands to relays or another aplications for home automation but for iphone i dont know an app for make this)I think it's easy and dont need libraries for use it and only need Arduino with one ETH shield.
I've been developing something similar, but with an Android. I've seen 1 or 2 apps on here that people have created but they don't seem to be updated much, and they don't leave much room for development.I can't say for certain how you can retrieve the IP info, but I don't think that would work because your IP is likely to change a lot on the mobile network. I can see blacklisting, but that might take a lot of work. To keep mine secure, I don't forward ports and keep the Arduino access to the local network. If I'm away, I just log into my home VPN and access the device from that.