What's unfortunate is that this pushes Apple to work harder to lock us out of our devices, since it all depends on jailbreak-ability.
Example: I want to be able to redirect calls to my existing number to an audio message that I've got a Google Voice number now. I can only do that by jailbreaking and hacking about.
Note that you will be charged as if your phone is dialing the GV number. When I was in the UK and had forwarding set up, I was charged the $1.79/min as people left me voicemails as if my phone was dialing the GV number.
Example: I want to be able to redirect calls to my existing number to an audio message that I've got a Google Voice number now. I can only do that by jailbreaking and hacking about.