I think for the OP; the "Find my iPhone" app is a moot point anyways. You have to install it before you lose it.
That being said; I'm not sure a wipe would get rid of it. You may not be able to remote wipe it; but you may still be able to track it depending on how the system finds it.
And I don't think you need a data plan. I installed it on an iPad I borrowed from work so I could setup my 3GS iPhones. The iPad does not have a data plan; but I could still track it.
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