AASTRA 6755i Installation Guide EN - Manual (Page 10)

4 Model 55i IP Phone Installation Guide
Phone Parts
A PoE (Power over Ethernet) inline power injector supplies 48v power
to the 55i through the Ethernet Cable on pins 4 & 5 and 7 & 8.
Warning: Do not use this PoE inline power injector to power other
devices.
The Model 536 Expansion Module (536EM) and Model 560 Expansion
Module (560EM) attach to the right side of the 55i phone. Model 536EM
provides 36 additional softkeys for the phone. Model 560EM provides 60
additional softkeys. For more information about the expansion modules,
see the section,
Model 536 Expansion Modules (536EM) on page page 25.