Welcome to the forums,
Sure, you can present different screens based on URL (and we are doing some more browser/device user-agent detection in 6.0).
So when /m/ or ?client=mobile :

vs / or /h/ :
There's a zip with a login.jsp & ZmMsg.properties attached.
They go in /opt/zimbra/mailboxd/webapps/zimbra/public/login.jsp & /opt/zimbra/mailboxd/webapps/zimbra/WEB-INF/classes/messages/ZmMsg.properties zimbra.zimbra 664.
The ZmMsg.properties (5.0.11) adds rememberMeMobile/splashScreenCopyrightMobile/clientLoginNoticeMobile, or put in your specific language file.
This is implemented in GNR (ZCS 6.0) via
Bug 18726 - Need iphone version of login page