
I was looking for a mount for my iPhone to keep it from sliding off the area where my cup holders are (and often it would slide between my seat and center console...a complete hassle to retrieve it!). I saw a few basic mounts, but was intrigued when I saw this Kensington version that increases the sound.
I have to say...it actually does work. The sound is noticeably louder when in the mount. I'm not sure how people will use this, but I've sometimes used it to listen to music or even take phone calls...both of these when I'm parked and waiting for my kids to finish practice. The sound isn't quite enough when I'm driving on the freeway, but in low-noise environments it works great.
The only con on this item is that the arm length is about 10-12", and my windshield is too far for that. But the vent mount option works great for my situation.
Highly recommended.

I've used it for a few months now. The suction mount is very strong. The arm is long enough that you can twist and bend it to fit your needs. I feel the arm clips don't really grab on to my iPhone but I'm satisfied it won't slip out. The big thing is the sound amplification which is why I bought it. Honestly I don't notice a huge difference whether I'm listening to Pandora or turn-by-turn directions.
UPDATE 6/6/2011: This doe NOT work for the iPhone 4. The sound on the iPhone 4 comes out of the bottom right speaker. The mount only takes sound coming out of the bottom left speaker. Other versions of the iPhone will work for the sound amplification.
Buy Kensington K39255US SoundWave Sound-Amplifying Car Mount--Compatible with iPhone 4-Black Now
Having been a volunteer EMT back in college, I saw enough accidents to conclude that there is no way that I want to cause or contribute to a car accident by paying attention to my phone rather than the road. I therefore usually find myself having to ignore calls while driving, or pulling over to pull out my phone. Needless to say, I miss a lot of calls while I drive. That makes my boss irritated.
I received this Kensington-made device today and was excited to give it a try. It took exactly 10 seconds to attach to my car's windshield. I was able to set it up in a location that in no way interferes with my view of the road an important consideration. I then attached the device using the climate control vent attachment and found that it too took a very short period of time to set up. I placed my iPhone 4 in the cradle, leaving it within its bumper case (I hate the case, but I hate dropped calls more...).
The bumper case did not interfere with fitting the phone in to the cradle. Surprisingly though, it also did NOT interfere with the enhanced sound quality that this car mount kit is supposed to offer. I placed three calls from the phone while it was in the cradle and found that the sound quality is MUCH better than when I hold the phone in my hand and use speaker-phone. The people that I called all said that I sounded crystal clear to them, and that they thought I was holding the phone to my head rather than using speaker-phone.
I'm a convert.
Please note that this is NOT a powered device. It does not require a power plug connected to the cigarette lighter, and does not draw power from your phone. It achieves the improvement in sound quality by collecting and directing sound rather than allowing it to radiate out in all directions evenly.
If you HAVE to take a call and do not have a bluetooth-enabled car stereo system, you should be using this device, or one like it.
Read Best Reviews of Kensington K39255US SoundWave Sound-Amplifying Car Mount--Compatible with iPhone 4-Black Here
After looking over reviews on a number of cradles I went with the Kensington K39255US. I was thrilled with the vent attachment and the sound amplification. At first the cradle lived up to all my expectations. After a couple of uses, the sound amplification wan't the same. One of the little rubber bumpers had fallen off at the bottom of the cradle where it meets the iPhone speakers. With the rubber piece missing half the sound isn't amplified. With one of the contact points missing, the cradle doesn't seem to hold the phone as well either. I couldn't believe the cradle would fall apart so easily. I looked at the other piece, the one that hadn't fallen off, to see how it was attached and the rubber just barely protrudes into a plastic cutout. I looked everywhere for the missing piece which was black and not much bigger than a pencil eraser. If I would have found it I would've glued it to reinforce the flimsy mechanical failure point.
The box says "The Kensington Promise" and that the cradle comes with a 2-year limited warranty with a url to Kensington's warranty website which says "product will be free from defects in material and workmanship under normal use and service for two years after date of purchase". That seemed "promising" so I contacted Kensington support with my problem. They apologized and told me that "We regret to inform you that these parts are not available for separate sales or replacements." That was it. No offer to replace the unit either.
I may try removing the other rubber bumper to see if the sound amplification and fit can be improved, I may also try fashioning a bumper replacement myself, but what I won't do and this I can "promise" is to ever buy anything from Kensington again.
It's a shame really, because the cradle is almost perfect. Perhaps the rubber bumpers were from a bad batch and normally they don't fall off or maybe the box should include instructions that the product requires some additional adhesive to prevent disintegration. I can't recommend this or any other product from Kensington unless you are prepared to buy a replacement if there's a problem with it.
*UPDATE*
After reminding Kensington about their warranty, they shipped me a replacement unit. The replacement exhibits the same loose fitting rubber bumpers, but I used some adhesive to strengthen the poor mechanical fit. Now the cradle is working as intended. I appreciate that Kensington came through with the replacement and once reinforced with adhesive the cradle really does work quite well. I would probably recommend this cradle, but with the caveat that the bumpers can be lost if not glued. Kensington needs to either improve the bumper connections or improve customer support. As it stands the customer support was a little too self-service for my liking. I personally still wouldn't buy from them again after this experience.
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Let me preface my review by saying this is the 5th iphone window mount I've owned in a few years. I use my iphone nearly daily for GPS travel and, consequently, I apparently wear them out quickly.
I gave up on window mounts awhile back after I finally got one that attached to my airconditioning vent...it was perfectly at the right level and didn't block my vision or advertise I had an iphone if I chose to leave it in the car if I wanted to pop in for some errand. So, while I use this one only with the vent clips again, I will add I tried the window mount just for the review and it worked very well if that's your preferred method. It snapped on easily and held well. As for the vent mount, I have the oddest vents in an unusual car and it adjusts to fit any size vent and air goes around it...it wont keep you too hot or too cold 'cause it sits at the vent mount, if you choose that.
Why this is my favorite mount for my iphone? Because it is, thus far, the ONLY one that allows me to slip my phone in and remove it with one hand...just clip in and clip out and the clips are on the side...important because it seems like those that hold it from the bottom primarily wear out easily...but, most importantly, regardless of whether I have a thick iphone case on it or no case, it adjusts automatically to still hold it tightly. The ones that just let it lay in the clip jiggle around and make it hard to read when using ipod or GPS...the ones that clip on very tight or require a special case to hold it to the mount, mean I can't use an iphone case or I cant't remove it with the flick of a wrist.
At first I only gave this product 4 stars because I didn't see any difference in the sound amplification. However, I was using a 3Gs on it at the time. As soon as I used the iphone4, I DID see that it amplified the sound. So it should be noted, if you have an iphone that is not the iphone4, it will fit perfectly in the holder and you can keep it charged as you use it since the bottom is open for your charge plug to connect. It will grip the larger phone just fine...but, if you aren't using the iphone4, the sound amplification feature will not be present. I like it enough that I'm still using it for both our 3Gs and iphone4. And, I should note, if you DO have the iphone4, you WILL notice the sound amplification feature engage.
this one is my favorite.
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