This is a bit of a shock. For the many users that are carrying around the HTC Arrive on the Sprint network, there is some fantastic news. The Arrive, much like its other HTC first generation brethren, are now fully unlocked thanks to the HSPL release. Per usual, this may ruin your warranty, bla bla bla, and if your phone heats on fire in the process, no one here at wpsauce is responsible. If you want to know the feeling of true interop unlock, go to the source.
Thanks Bryan for the tip!