Quick Dial changes dialled symbols to another you need.
Ex:
you dial #1 -> the system dials *4001 instead of it
you dial #2 -> the system dials *4002 instead of it
you dial 0 -> the system dials 9 instead of it
System Speed Dial (SSD) is like a system phonebook - it doesn't modify your dialling, it just dials the number stored in corresponding cell.
Ex: you dial **XXX -> system dials number from the cell No XXX
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If you set CLI-destination next to the number in SSD cell and CLI feature is enabled for DIL or DDI, incoming call from that number will not be distributed by DIL or DDI scheme but it will be distributed to CLI-destination.