*Points at the Network Edition, as you're supposed to leave license blocks/copyrights intact on the Open-Source Edition. (To answer your question about removing the extra wording, if you have purchased NE then yes it can be modified.)
If you're testing on 5.0RC2 add to
bugzilla as needed, however if your on 4.5 just wait, as the login screen has undergone some
significant changes - essentially a total recode.
(BTW this is the
Zimbra Mobile OTA section)
standard web-client mobile web-client