Apple has no authority of the use of "i" before things. If it wasn't legal, they'd have a cease and desist letter just like CoinyeCoin. However, they haven't received one, because it's perfectly legal.

Trust me, this isn't a new topic. Read up on trademark law and various news stories regarding the use of "i" on non-Apple products. Generally speaking, it's fine - though if you're going to create a phone and call it "iFone," you're going to get sued.