Subdomains are not automatically created as DNS system, which is running Internet name to IP address mapping, is controlled outside HTTP server.
Please contact your hosting administration regarding how to enable subdomains.
For more information please read
en.wikipedia.org/wiki/Domain_Name_System
However, Mobilejoomla! should automatically show you iPhone template if 1) your hosting supports what it takes to run TeraWurfl handset database 2) you have correctly configured Terawurfl. Template selection can happen independent of the domain name when handset database is enable.
www.mobilejoomla.com/wiki/FAQ