To answer your simple question the camera won't use any (much - some tony amount of polling data I think) internet traffic when it is just sitting there and you haven't logged on to the camera via mydlink.com or via your iPhone. Its not sat there all the time streaming images to the internet just waiting for you to watch.
Under the /video.htm page (probably in your case 192.168.1.104/video.htm) you can set the resolution of the images and the FPS (between 1 - 30). I've got mine set up with a similar intention - just the odd glance into my house when I can be bothered, nothing fancy.
I did leave my mobile set to watch the home streaming for a bit when I first got it - and got a warning letter from my mobile broadband provider about data usage :-)
If my maths is right, if it was streaming permanently at the bit rates I'm using (320x240 resolution, about 10fps over my broadband, which generates an 8KB image for every frame) daily use would be:-
8kilobytes = 64kilobits x 10fps x 60secs x 60mins x 24hours = 55,296,000 kilobits in a day (over 52 gigabytes of data transfer), so every user would be swamping their broadband every month!!
Hope this helps!
Matt