the e90 has a built in SIP client just like the e61..so yes it does voip.. you'll need to sign w\ a voip provider though.. I use truphone.com and its the easier install..they got a cool intro offer now of free calls and a pstn number through march and just announced you can talk w\ googletalk users, there is also challengermobile but that does pure SIP and free.. GIZMO will work as well..
btw the n80i comes w\ gizmo preinstalled - not fully running on it...