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I'm sure there's a plethora of thread about this already.
But to answer your question, yes it is possible, using PwnageTool 4.1 if you want to unlock with ultrasn0w. If not, then you can also use greenpois0n or limera1n.
Use google to find the tools and instructions you need, redmondpie has a good guide for PwnageTool.
 
Most internet sources suggests that 3.1.3 is better than 4.1.

the 3G reaps little from the upgrade to 4.1, so I would suggest staying on 3.1.3

Thanks. After my money settles down, plan to nab a iPhone 4, but there are a few apps I've been eyeing that require 4.0+. But not enough if it's going to drag the phone down too much.
 
Thanks. After my money settles down, plan to nab a iPhone 4, but there are a few apps I've been eyeing that require 4.0+. But not enough if it's going to drag the phone down too much.

Chances are if the app requires 4.0, the 3G will run it pretty poorly. You're right in waiting for your iP4, you'll get a BIG kick out of it if you're upgrading from a 3G (that's what I did).
 
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