Hi Ben

That's an interesting question. The .mobi domain is aimed at providing content that will work on mobile devices. However, you can serve up whatever markup you like, as long as you know that the device supports what you send it.

To put this in a slightly different way, if you don't know what kind of content the requesting device is capable of supporting, then you should send XHTML MP, since there is a good chance that this type of markup will be supported.

Thus, if you know that the requesting device is a desktop browser, well then you can send whatever you like to it, even if it's on a .mobi domain.

So you don't necessarily need a separate domain. However, if there is a large desktop component to your application, it might be better to have that on a .com URL.

Thanks for the reply. For some reason i didnt get email notification of the thread so just checked it now. Im building a .mobi site for mobiles but i guess i will detect if its a Desktop to redirect to a .com specific site for Desktop.

I think the most important thing to remember is that you should give the end user the choice of being redirected.
The user may well have gone to your mobile site on purpose - the last thing you want to do is annoy them by showing them something they explicitly did not ask for :)