Every time one gets a website done thinks about the old browsers. What can be done with the users who visit your cool, trendy new website via an old browser.
Well there pretty cool options for this.
1. You can have a message displayed like Facebook does for IE6 and other old browsers initiating them for using upgraded browsers in order to view the site properly.
2. Have another home page for old browsers like this site does. http://www.chakra.org/
For IE6 visitors you may have the default theme. Same you can apply for mobile phone visitors as well in case you don’t have the mobile theme.