Yes that's a shipped/stock rom. DONT re- LOCK IT, unless you have to take it back for some reason. keep it unlocked if you are going to be flashing custom roms.
Good find on that post gravity, that will help us-cellular users a lot. Step 6 and Step 7 should help you out if you flash a custom rom that isn't set up for you but most will be.
Try out RaidZero's roms. Psyki is also great but its pretty old, if you want newer builds go with raid's. Plus its super fast and stable it is INSANE.
http://www.ppcgeeks.com/forums/showthread.php?t=81038