There are a few options available, but as of right now there is no live tv streaming on the iphone
1. Joost- is a free app that allows you to stream videos, tv shows, music videos and some other stuff. But only works over wifi and has a limited selection.
2. youtube app- I know a lot of it is useless junk, but a lot of tv shows can be found on there, granted it's never in one full clip, but in 2 or 3 clips you can watch a full episode. and that obviously works on edge/3g/wifi
Who knows when if ever, but hopefully slingbox will someday work on the iphone, then you will get live tv streaming. Here is the link for the discussion on when or if ever it will work on the iphone
I don't have personal experience with OrbLive but as I understand it you are able to use your compatible tv tuner on your PC and stream the video to your phone.