Even if you get the proper power brick, what is your intent for the phone? the phone by itself is a dummy terminal and will not do anything unless it can register with a PBX/Proxy. Will you be registering it with a specific SIP server or will you be installing a PBX such as Cisco Communications Manager, etc?
Hi Mandy, Buying the power supply will only power up the phone.
Now you need a dial tone. The Cisco ip phone would need a call manager to boot up and get a dial tone and a number assigned to it. This is the scenario in normal office environment.
Outside your office since you don't have a call manager, you need a services provider and your IP service provider should be able to register it to their server using SIP protocol (generally) which is a bit more complicated and does not work out of the box. You have to check with them how they would register it (using a VPN ) / etc. in any case you would need a tftp server to get the SIP Firmware and pass the username and password etc.
In such scenarios, You would be better off using other phones like grand stream / polycom after checking with them for the recommended model if they don't support Cisco.