Making a 'mobile/cell' version of a PHP/Javascript website?

[sardar]

I'm about to potentially start work on a website, but the client has a requirement that the website should also be accessible from mobiles/cell phones. He hasn't mentioned which mobiles he wants to support in particular but I assume it would be smart phones like iphone, blackberry, android, etc.My question is, how much work will this take? For example:1) Will I need to make two copies of the site, one for computers and one for the mobiles? Or even build 2 copies of all the html files?2) Are there any special considerations I need to keep in mind when using javascript/ajax? Such as any features which may not be supported on cell phones (such as jquery)?3) Is there an easy trick for supporting the site on both computers & cell phones? Like just showing a different stylesheet for cell phones and everything else would just work?Thanks.