AASTRA 6757i Installation Guide EN - Manual (Page 10)

4 Model 57i IP Phone Installation Guide
Phone Parts
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 57i 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 and 560 Expansion Modules on page page 24.