Everyone knows about 3G and now 3.5G; it lets you surf the Internet on your mobile phone and even watch video clips. So when the word mobile TV starts floating around, it easy to get confused.
Mobile TV refers to watching TV on your cellphone. Usually, it refers to the use of a digital braodcast technology instead of cellular technologies like 3G.
The main standard use in many developed countries is Digital Video Broadcast Handheld (DVB-H) technology. The phone needs to have a receiver chip to receive the TV broadcasts. When such broadcasts go commercial, anyone with a phone which has the DVB-H chip will be able to get the mobile TV service.
As DVB makes use of broadcast instead of streaming technologies like 3G, video quality is better and less jerky. The cost is also lower since you do not pay for every kilobyte used.
Whike DVB-H is for small devices like mobile phones, its cousin DVB-Terrestial (DVB-T) is for viewing on larger screens like the TV Mobile channel on busses
DVB-H (thanks for the correction Tuija) broadcast on a Nokia mobile phone.