The VAIS needs the navigation system installed.
I have a 2002 w/o navigation, and there's a product from GROM that will work with it. Last time I played a CD was in 2005, so not a problem for me. Also, if you want to sell the car you just hook the CD back up.
http://www.gromaudio.com/store/bt3_adapters/toyota_lexus_scion_98-11_aux-in_mp3_bluetooth_ipod_iphone_adapter.html
The down-side, if you consider it one, is you lose the CD changer. The GROM interface connects to existing wires and replaces the CD.
Check out the compatibility chart here: http://www.gromaudio.com/grom_application_guide.pdf
User manual for the BT interface here: http://www.gromaudio.com/docs/instr_bt3.pdf
I actually ordered one last week, they had a $20 coupon, should get it this week and install it.