I wanted to make a cheap mount for my iphone and did not want to spend a lot of money. I also did not want a window mount one at this time. I found an iwave car mount kit at TJ Maxx for $15. (apparently this place has some cheap electronic stuff along with their horrific clothes) I cannot find a link for the iwave mount kit online, but it is similar to
this one. The vent brackets were not long enough for our round vents so I changed it up a bit and figured I would share.
Started with the mounting kit and some black pull ties.

Slid the legs in the vents and let the third one just rest on lip of vent. Fed the ties in through each side and pulled through back of vent and back up. There are thin plastic connectors in the back of the vent, you could loop around these but it still swiveled too much and could break them. I avoided them.

I added a third tie on the leg that sticks down, otherwise the whole thing swiveled too much in the car. This one keeps the whole unit from just spinning or flopping on side on turns or rough roads.

Trimmed the excess pull tie off.
Once mounted it it works really well, I was actually surprised. The iwave has a button in the back that opens the padded arms that hold it. Very quick to get in and out.
Pros- Mounts below radio which I like. It is pretty stationary on regular roads. Could text or whatever without it moving around. You can loosen/tighten the actual holder so you can swivel the whole thing sideways and tighten. Will be useful when full GPS is avail for iphone.
Cheap and easily removable with a pair of scissors.
Cons - Obviously blocks vent and on rocky roads it may move some.
If you use the aux in the wire coming out the top of the phone can get in the way of the left knob.
May be too low for some people.
Makes it a little too easy to just pop open jeepforum.com on long drives to see whats going on...
Sean