If you can tether your iPhone, you should be able to connect to a TiVo network adaptor. Since your 'net access to the TiVo won't be "always on" you'll need to manually connect to the TiVo network periodically.
If you can't tether your iPhone and your netbook has a wireless card on board, you may be able to create an access point through it connecting your TiVo with your AT&T card.
If you can't tether your iPhone and your netbook has a wireless card on board, you may be able to create an access point through it connecting your TiVo with your AT&T card.