Cisco SPA 504G Owner's Manual page 43

This diagram depicts your setup options. By purchasing the optional
Wireless Transmitter and Wireless Adapters you may also connect Desk
Phones wirelessly.
The following setup options ARE NOT supported:
1. Connecting one phone to another
2. Connecting a phone to the base unit then connecting a PC
3. Connecting a phone to the base unit wirelessly and then connecting
a PC
4. Connecting a PC to the base unit
5. Connecting a phone to a router that is connected to another router
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