One note about the speakerphone: when a call comes in, your music will pause and then resume when you hang up the call. To use the speakerphone capabilities you do have to be in Bluetooth mode rather than have your iPhone docked.
In its marketing material JBL talks up how the system delivers 30 watts of amplification to each of its four transducers "for crystal-clear high-output sound" and boasts how the "Ridge tweeters and Hercules woofers with computer-optimized DSP equalization deliver impressive frequency response (20Hz--20KHz) and minimal distortion, even at high output levels."
A lot of times products don't live up to the company's marketing language, but in the case of the OnBeat Xtreme, it really does sound good for its size. Stereo separation is always a problem in speaker docks where the drivers are only separated by a few inches, but this system does play very loud and delivers good clean, balanced sound with tight bass.
I tested the JBL in a couple of rooms: our larger audio-testing room and my office. It played so loud in the office that I got complaints from the woman who works in the office behind me and had to turn down the track from "The National" that I was playing.
I ran a bunch of different music through the speaker using an iPhone and iPad, both streaming music wirelessly and through a wired docked connection. I have some lossless test tracks we use for testing speaker docks and headphones, and those tracks didn't sound quite as good when I was streaming them wirelessly over Bluetooth, but most people will be barely able to tell the difference between a wired and wireless connection, especially when streaming standard MP3 files with modest bit rates.
Overall, the sound was comparable to some of the better speaker dock systems we've reviewed. Those include the Bose SoundDock 10, which retails for $600 and doesn't include Bluetooth (you have to buy an optional Bluetooth adapter for $150), and the Bowers & Wilkins Zeppelin Air, which also goes for $600 and which supports Apple AirPlay. Neither of those speakers offers an iPad docking option. Neither does Monster's Beats by Dr. Dre Beatbox, which does sound quite as good as the JBL but delivers a bit more in the way of bass and costs only $320 (it started out at $449.99 but has dropped). However, the Beatbox is missing a built-in Bluetooth option.
If you're OK with the JBL's design, the only downside to the product is really its price: it does cost $499.99, which is a lot to pay for an iPad/iPhone/iPod speaker system. But if you can get over that fact, you are getting a high-quality, impressive-sounding speaker dock that also features Bluetooth wireless streaming and speakerphone capabilities. And, oh, you can dock and charge your iPad, which is an important feature for a lot of folks.
Put it all together and I have no problem recommending the OnBeat Xtreme, though I think JBL would find many more customers if it could somehow get the price to $300 or less.