how to get sub domains to work with $live_site

My joomla config has a mod that's used to make some things work. We have

$live_site ="www.mydomin.com'

it seems this is conflicting with the subdomains routing to iphone or pda. Causes an infinite loop.

How do i get subdomains to work with this mod?

Just tested MJ on fresh Joomla with changed $live_site in config, and found no issue.
Do you use redirect in htaccess or sef-extension that may do such a redirect?