Apple = control + monopoly. If they don't have the full control of something, they destroy it, that's why they do everything they can to stop hackintoshs, jailbreaking and iPods without iTunes...
What is google voice? Call screening, Listen in, Block calls, SMS, Place calls, Taking calls, Phone routing, Forwarding phones, Voicemail transcripts, Listen to voicemail, Notifications, Personalize greeting, Share voicemail, Conference calling, Call record, Call switch, Mobile site, GOOG-411, Manage groups, ...
Have you any idea how much money carriers make with these services?? If google offers them for free they are screwed and according to apple the moon will crash on Earth and there will be a tsunami killing 3/4 of the world's population! Carriers should only provide bandwidth and a number, the rest should be done over IP with what you want, so you only pay for the bandwitdh you use.