There are some people thinks that video streaming could be a big hit on mobile phones, but I don't think so, at least not in the near future. The near future means two years time, three years time, or longer, depends on how the technology grown.
There is a few reasons why I said so.
1. Bandwidth. To perform video streaming, need a lot of bandwidth, and bandwidth is always limited. Even 3G has a broader bandwidth, but wireless capabilities always limited by location, implemented infrastructure. We don't always get the ideal bandwidth, lagging video is common when we stream on mobile network, even on 3G network.
May be WiFi and WiMax can provide a faster video streaming, but we might be referring to a different device from mobile phones for accessing the internet using WiFi and WiMax.
2. Screen size. Mobile device display is getting bigger and bigger, but watching video on a small screen size is not a good experience, especially when you compare it with the large display like iPhone. iPhone is a good mobile device for watching video, but iPhone is the one and only product from Apple, there are a few other mobile phones which came with large display screen size like HTC diamond, but majority of the mobile phones still came with a smaller display.
A device with a 3.5 inch display are too big for many mobile users.
3. Battery life. Today's mobile CPU is good enough to process video streaming, but when you put in more functionalities into a mobile phones, build a bigger screen, it consume more power. A good example will be Nokia N95, it was marketed as a mobile PC, can browse internet, send email, it even cames with GPS, but it drain the battery too fast. Two of my friends get a N95 but can't wait to sell it, because the one day battery life for their normal usage doesn't meet their expectation.
Battery technology will improved, I believe so. I have heard about it since 5 years ago, but it still can't meet most people expectation as for today.
A mobile phone is a device for you to carry around to make phone calls, or receive phone calls. If a mobile device is too big, or the battery life can not last for a day or two, it defeat the purpose of being a mobile phone. iPhone is a good device for video streaming, but is still new and yet to be proven.
I believe the day video streaming on mobile will come. For today, let text application on mobile phones and video streaming by another portable media player device, it sounds more practical.