Nagroid is a mobile client that speaks to nagios via http/https licensed under GPLv2.
The client will let you configure category aware notification sounds for either Warning Alarms, Critical Alarms or Down/Unreachable alarms and allows you to filter handled problems.
This app goes along very well with ConnectBot (GPLv3) if https/https access via SSH tunnel is required.
Pretty neat, but I guess the xmpp notifiaction is more practical to me when it comes to Nagios.