I'm guessing given the nature of the question, the person wants to use PoE rather than a power brick...
I've heard good things about powerdsine power injectors. SPA series seems to use standard PoE so chances are, anything is likely to work. There is a PDF floating around with power consumption - they are low enough to work with anything though.
You are able to use either the power adapter specifically made for the phone or a PoE Injector. I would be inclined to use the PoE Injector becuase you can use w/ any PoE device and not a specific phone model. You can also pick up a PoE Injector at one of the big box computer stores(in use Fry's or Micro Center).
Any PoE injector should work due to PoE being a standard and I have personally used the PoE Injector on the SPA504G and SPA525G phones when a PoE switch failed, so they are great to have handy.
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