When you buy all Cisco IP phones, without the power adaptor, so how to work?
There are 3 options for connections.
1) Buy power transformer (CP-PWR-CUBE-3) directly; suitable for few Qty, will be an economic method.
2) If you have POE switches, will be better. Connect by a RJ-45 cable directly.
POE switch: e.g. WS-C2960-24PC-L (24 Ports), WS-C2960-48PST-L (48 ports) and so on.
3) For long-distance consideration within 100 meters, you also can connect with Power Injector (CP-PWR-INJ).
More Cisco IP Phone Tips:
How to Configure a Cisco Unified IP Phone 7921 with Call Manager Express?
Cisco to Update IP Phone Capabilities for Its Enterprise Users
