Functions such as transferring calls using a Transfer key require the user to have at least one available call appearance button in order to complete the outgoing call part of the process. However, by default all call appearance button are available to receive incoming calls at all times. Through the system configuration it is possible to reserve the user's last call appearance button for making outgoing calls only.

1400, 1600, 9400, 9500, and 9600 Series telephone users can put a call on hold pending transfer if they already have held calls even if they have no free call appearance button available. See Context Sensitive Transfer.