I want to start a radio service on my website.i want to know is there any company which is offering services regarding to this ??
If yes, which one , and if no , then what is the way ? Is it possible to launch a radio service on some hosting company? or i must have my own hosting in order to start online radio

One of the easiest ways to start your own Internet radio station is to use something called ShoutCAST which works in conjunction with Winamp to broadcast your voice to the world! You do have to have your own hosting and the amount of bandwidth used is colossal, you have been warned! You can find out more information here.
Most companies will not offer a free service to host Internet radio, and the costs of a paid service are huge, due to the amounts of bandwidth needed to get many listeners at a good quality.

Add to bandwidth:

Streaming audio can consume vast quantities of bandwidth if the MP3 servers' bit-rate is set too high.

Consider this scenario. A T1 link has a capacity of approx. 1.55 Mb/Sec. If you stream your MP3's at 128K/Bps stereo, each connecting player will use 256K/Bps, so only 6 users could connect to your MP3 server at any time without problems. And at 256K/Bps, you will not get too many modem users connecting!

So you must make a decision at what to set your stream rates not only on what your server's internet connection is rated at, but what your users will be connecting at. 24K/Bps Stereo will give a reasonable quality signal that 56K modem users will be able to connect to, and for the same T1 line would allow approx. 32 simultaneous connections.

If your server is running on an Intranet, bandwidth issues will still have to be considered especially if your network is running 10M/Sec.

But please let either your ISP or sys admin know you are going to stream otherwise you may be in for a shock. Some ISP's will charge you for bandwidth over a certain limit and sys admins like to know why their network is now running slow

But it's up to you
That's all !

Not to be off-topic, but lol, rob, you still have a sig from christmas of last year. That's like leaving your christmas lights up year round.

As for the topic, I'm not sure of any sites or companies that offer radio services, but I would also be concerned about bandwidth and even space issues.

EDIT: oh, nevermind, it's a sig rotator. still funny though.