I was one of, if not the first to order the VAMP through V-MODA's official website once it was put up for sale after months of rumors, speculations and advertisements. Featurewise, VAMP is a very unique product in many ways, and I'd like to discuss its functions and capabilities compared to other portable DAC's, amps, or DAC/amps before sharing my impressions.
 
First of all, VAMP is a portable DAC/amp for the iPhone 4/4S, but that doesn't mean its usage is strictly limited to an iPhone 4/4S. Although they won't fit into VAMP's case physically, you can also use other iDevices such as an iPod (including iTouch), iPhone 3GS, or iPad by with VAMP via a sync extension LOD (line out dock) cable . Of course, VAMP should still be used primarily with an iPhone 4/4S as it was meant to be for maximum comfort and portability. So if you don't own an iPhone 4/4S and isn't planning to get one, then VAMP will serve you little or no purpose.
 
VAMP is special in a way that it bypasses the in-built DAC of iDevices and utilizes its own DAC for better hi-fi performance. As far as I know, there are only three other portable devices capable of this feature: Cypher Labs Algorithm Solo (DAC only), Fostex HP-P1 (DAC/amp), and VentureCraft Go-DAP (the model which VAMP was based on). Most so-called DAC/amps, such as Fiio E17, aren't capable of this, because the ability to take the pure digital data out of an iDevice through LOD costs the product Apple's license fee. That explains why gears like HP-P1 or VAMP are a lot more expensive than other portable DAC/amps.
 
To summarize VAMP's functions:
#1. A solid case for iPhone 4/4S, protecting it from scratches (although it would break my heart to see my $650 VAMP damaged instead)
#2. Extra battery for an iDevice, doubling its life
#3. Takes pure digital audio data out of an iDevice via LOD
#4. Outputs digital data from #3 via mini-Toslink optical S/PDIF (fixed to 48 kHz) with digital-digital coversion to another DAC, effectively serving as an iDevice dock
#5. Converts digital data from #3 to analog signal via VAMP's in-built DAC, amplified through VAMP's headphone amp section with volume control and 3.5 mm headphone out
#6. An equalizer function (aptly named VQ mode) which enlarges 3D soundstage and add some bass to music, making some closed-sounding or bass-weak recordings more enjoyable... YMMV.
 
FYI, VAMP is a fully upgraded, uber version of the Japanese company VentureCraft's Go-DAP Unit 4.0. So it's made in Japan, but should be overall better than the default Go-DAP, at least in theory.
 
Also, I purchased the VAMP at $650, but right now it's also on sale at Amazon for $600.
 
Before actually reviewing the VAMP, some caveats and disclaimers: this is the first time I'm doing a full review for an audio component, so please excuse my bad writing. This is a subjective review, after all, and my ears aren't really the best measurement tools. Also, VAMP happens to be the first portable amp - or DAC/amp, for that matter - that I've bought, so I didn't have much opportunity to compare it to other similar products. For the sake of review, however, I was able to borrow a Fiio E17 and a Hifiman HM-801 from a couple headphile friends. I wish I could've compared it to something like a  Fostex HP-P1 to level the playing field, but unfortunately I couldn't find one around. So without further ado, let's get down to it.
 
Unboxing, Design, and Build Quality
 
The VAMP arrived in a sleek box like most V-MODA products. You can check out Val Kolton's (owner of V-MODA) cool unboxing video of VAMP, which involves boats and choppers and other gimmicks. Included in the box were VAMP itself, a mini-USB to USB cable, and a user-friendly instruction manual. The USB cable can be used to charge VAMP alone, both VAMP and iPhone, or iPhone only. With the latter option, you can also link your iPhone to a computer for streaming data as well.
 
VAMP looks gorgeous in real life as its pictures are. Snap an iPhone into it, and it makes an awesome-looking combo for portable use. I've carried it around outdoors, and it sure was an attention-grabber for many friends I ran into. As for build quality, it's build like a tank as most V-MODA products are. I was too afraid to test it by dropping it or throwing it around, but it felt very sturdy, almost military-grade. In short, build quality is top-notch.
 
Overall, with nearly double the thickness and weight of an iPhone alone, the iPhone/VAMP combo looks like a badass iPhone on steroids.
 
Sound quality
 
I mainly used my Crossfade M-80 (V-MODA's current flagship headphones, soon to be replaced by M-100 over-ear headphones) for this review, but also an AKG K 550 (on loan) and even my Audez'e LCD-2. I compared VAMP to various portable and desktop gears, including Fiio E17, Hifiman HM-801, and my high-end desktop system costing over $4,000 sans cables. I had a couple music playback softwares for the iPhone, from the default player to the well-received Capriccio and FLAC Player.
 
Compared to listening directly via my iPhone's headphone out, the improvement from VAMP was significant. I had been slightly worried that I may not hear a lot of difference, for two reasons. One, V-MODA's M-80 is a highly sensitive headphone which can be efficiently driven by anything, even an iPod. Two, some Head-fi'ers have pointed out that the VentureCraft Go-DAP (the model VAMP was based on) didn't make a serious improvement with an M-80. Well, I'm happy to say that my fears turned out wrong, because I was pleasantly surprised by the unprecedented power and liveliness of music coming out of my M-80. There was an extra level of clarity, as if a veil had been lifted from the music, as well as satisfyingly punchy - but not loose, bassy - bass. 
 
I was also impressed by VAMP's VQ mode. In fact, as I spent longer time with VAMP, I found myself using VQ mode more often than the default, neutral-sounding Pure mode, because VQ adds a level of spaciousness and juiciness that makes music more satisfying, at a slight loss of fidelity to the originally recorded material. For some recordings that already sound too spacious, however, using the VQ mode may cause them to sound overly spread out and thin. While I had previously appreciated Capriccio's 3D equalizer feature, using that and VQ mode at the same time made music sound too loose. But then again, it helped with a few songs that sounded too "closed." Your mileage will vary with this one, but it's always a good thing that they're giving us a choice based on our preferences.
 
I tried using VAMP as a iPhone dock by connecting it to my desktop rig DAC via an optical cable (as I mentioned above, this is fixed to 48 kHz). Compared to my iMac running Pure Music with April Music's Stello U3 converting asynchronous USB to coaxial S/PDIF, I knew it couldn't be a fair comparison. As it turned out, VAMP as an iPhone dock sounded flat compared to my dedicated Mac-based transport. But honestly, the difference wasn't that huge, and when I used the default iTunes instead of Pure Music to level the playing field, the gap was lessened. I'm not sure if many people would actually use VAMP as an iPhone dock, but it doesn't hurt to have an extra feature. In fact, if I had already had an iPhone dock like VAMP, I probably wouldn't have bought another computer that costs a lot more.
 
Compared to sub-$200 Fiio E17, the $650 VAMP was downright superior in many ways. The Fiio E17 can't even take advantage of its own DAC when using with an iPhone, so it wasn't really a fair game from the start. The best way I could think of to A/B these two was iMac/E17 vs. iPhone/VAMP. While both rigs boasted decent clarity, the latter combo sounded more immediate, forward, and stronger in bass punch. VAMP wins, hands down.
 
Vs. Hifiman's HM-801, this was a rather difficult comparison. HM-801 is more expensive than VAMP alone, but the iPhone/VAMP combo could cost more depending on the contract with your mobile company. In terms of outdoor convenience, the VAMP clearly wins because it holds both a cell phone and a DAP (digital audio player) in one box, whereas HM-801 is only a DAP and you'd have to carry a separate phone. Sound quality-wise, I cannot say that one is clearly superior to another; they simply sounded different. VAMP sounds forward, energetic, and juicy while HM-801 sounds laid-back, sweet, and spacious. Overall, when it came to fast-paced music like mainstream pop or rock, VAMP was my favorite, while I liked HM-801's presentation of more audiophile-oriented music like classic and jazz. As a college student, I listen to more mainstream music outdoors, so I ultimately preferred VAMP to HM-801. I guess it all depends on your musical tastes.
 
Now, compared to my main desktop rig... there was no comparison, really. I'm not saying that VAMP was vastly inferior to a multi-thousand dollar system, it's just that VAMP and my desktop amp, Schiit Lyr (with upgraded tubes), were meant to drive entirely different headphones from the start. Lyr is a high power hybrid amp designed to drive low-sensitivity, hard-to-drive headphones such as orthodynamics from Audez'e or Hifiman. It's what I've been using to drive my planar magnetic Audez'e LCD-2 for several months. Still, I plugged the M-80 into Schiit Lyr and let the music flow... only to realize my 6 watts at 32 ohm per channel amp was overkill for such highly sensitive cans, and even made hissing noises.
 
This time, I plugged the LCD-2 into VAMP too see the how far VAMP's potential goes. As expected, I felt VAMP slightly lacked sufficient power to drive the LCD-2 to its fullest, in contrast to the monstrously powerful Lyr. Even so, the relatively high sensitivity of LCD-2 - for an orthodynamic headphone, that is - made it possible to enjoy it with rather favorable results. I forgot to mention above, but the VAMP has two gain settings you can toggle with a simple tool. While M-80 sounded pleasant enough with low gain, the LCD-2 noticeably benefited from high gain setting. But then again, LCD-2 is a full-sized headphone weighing over a pound, so I don't think a lot of people would bring their LCD-2's outdoors. For most portable headphones VAMP was intended for, I think low gain setting is good enough.
 
The other headphones I've tried with VAMP was AKG's K702 and K550, the latter of which was released less than a year ago. The K550, albeit less expensive than the K702, was better than K702 in many regards and I personally consider it AKG's new flagship model. What I didn't like about the K550 was that it somewhat lacked PRaT (pace, rhythm, and timing) factor, otherwise it would've worked well with mainstream music. However, the VAMP makes up for its shortcomings by boosting its bass and overall energy. While I still prefer M-80 (and possibly, the M-100 in the near future) for mainstream pop and rock, the K550/VAMP turned out to be a great all-around player that excels in nearly all genres of music. The K550 is light and comfortable enough to be carried outdoors for portable use, so the K550/VAMP would make a decent portable rig for most people.
 
Value
 
Now, as for VAMP's overall value... is it really worth $600? Even if you are an iPhone 4/4S user - otherwise you'd have no business with VAMP and won't have read this far - is the price tag of $600 at justifiable for everything it does? Strictly from an iPhone 4/4S owner's point of view?
 
My answer is yes and no.
 
Yes, because it is a "portable" DAC that actually bypasses iDevice's in-built DAC circuitry, a decent headphone amp with high-low gain and equalizer settings, and an iPhone dock. Considering all that it does at a cheaper price than Fostex HP-P1 and HM-801, and being a lot more versatile and multi-featured than CLAS which is slightly less expensive, I think it's a great deal value-wise.
 
And no, because VAMP is not completely future-proof. I purchased my iPhone 4S some months ago, and I'm sure I'll stick to it for the next couple years, but what happens after that? I'll have to change my cell phone one way or another someday, and by then VAMP would have become obsolete. But by obsolete I mean obsolete for sales, as I'll still be using iPhone 4S/VAMP combo as a dedicated DAP.
 
Think about it, there are already many people out there who carry both their cell phone and a dedicated DAP like HM-801 or Colorfly. VAMP was designed as a product for the present, but even after iPhone 4S gets discontinued in the future, why not continue to use it as my main portable rig? The only edge it will lose after several years is its convenience factor, because once I get a new phone I'll have to carry two devices at once.
 
Verdict
 
Overall, the VAMP is an awesome gizmo for an iPhone 4/4S users with excellent build, design, and sound quality with a set of decent features one can hope to get from such a small, portable device. The price tag of $600 may seem questionable for some, but I believe it's justified considering everything it does and does well. Of course, VAMP is a niche product that may be discontinued once iPhone 4S is discontinued in the future, but that doesn't mean you can't continue to use it as a dedicated DAP for outdoor activities. For now, I'm really happy with my new toy. Kudos to V-MODA for coming up with such a kick-ass device!