Before you drop the bills for the no-contract price, check out the reports from other users on the efficacy of Yellowsn0w. For those who don't know about Yellowsn0w, its the Dev-Team's un-locker for the iPhone 3G. I wrote about it (with video) a week or so ago, before the release. There have been some mixed results, but the crack looks successful overall, and improvements are being made.
The blog post requesting user feedback has a misleading title: Don't eat yellowsn0w. Don't worry, guys. The hack is good. They had to use that phrase at some point, didn't they?
It goes without saying that I'm not recommending this and that any financial loss, technical problem, bad juju, etc... is on you, right? Good.