If you are powering on the system for the first time after installation, use the service processor serial port to power on the system and run POST. See Log Into the Service Processor Using the Serial Management Port.
If the network management port has already been configured, you can use it instead of the serial management port. See Log Into the Service Processor Using the Network Management Port.
Sun SPARC Enterprise T5440 Server Administration Guide
Integrated Lights Out Manager 3.0 Supplement for the Sun SPARC Enterprise T5440 Server