There are plenty of reviews detailing the phone's basic service and functions. The scope of this review will focus on the g'zOne's media capabilities and similar features.
First and foremost, the g'zOne Boulder does not include any computer connectivity. Upon research, I haven't found any suitable cables for syncing data between your computer and the phone. I believe Verizon purposefully obstructs the protocol that would allow you to directly access your phone's internal memory via USB connection. There is a way to sync music, but only through a proprietary service in connection with Verizon. Likely, Verizon wants it users to pay for its proprietary media services in order to access licensed audio and video. There are quite a number of features that redirect the user to these services. The phone includes virtually no applications or example media by default.
The g'zOne supports audio playback of MP3 and AAC audio. (including license-free files) MPEG-4+AAC video playback is also possible. (the files must be encoded as 3GP) The video player supports two types of display: a small frame within a player window that displays playback buttons, and a full-screen mode that displays the picture vertically. The playback of audio produces very bad quality through the phone's speaker. It's suggested you use a pair of headphones, or a headset. The phone does not include a 2.5mm or 3.5mm jack, but instead has a 2.5mm jack attached to an included extension. You will likely need to purchase a 2.5mm to 3.5mm converter.
Given the difficulty of transfering media files directly to the phone, the user has to jump through hoops in order to customize their media files. There is the option of e-mailing media to your phone, but any media content transferred this way will be downcoded by Verizon along the way; so it's not recommended. Since the phone supports microSD cards, the best way to transfer files is to load them directly to your microSD card from your computer, and then insert the card into your phone. A 1 GB microSD card and a USB card-reader should run no more than $10, shipping and all.
For audio playback, I encode my files with LAME at VBR 224. (or quality setting v1.50) I encode movies using 3GP (MPEG-4+AAC) at 320x240px resolution and 15 fps. This produces fair quality for the phone, and takes advantage of the screen's full resolution. A full movie encoded at these settings may be roughly ~200 MB.
Recommended encoders: lamedropXPd for audio, DVDFab6 for ripping DVD-VOB, Join VOB Files Tool to join split-VOB files after ripping, and MediaCoder Mobile Phone Edition for encoding video to be stored on the phone. (Google them, since I doubt I can post links here)
As for custom wallpapers, these should be at a resolution of 240x275px; otherwise, the phone will attempt to resize and crop them very unevenly. Although the phone has a larger resolution, wallpapers must be smaller to account for the heads-up display that occupies a portion of the total screen.
As a media platform, it's fairly efficient as long as you have a card-reader, and don't mind going through the extra trouble to transfer files. It's definitely handy to have your music and movies on-the-go, in case you're stuck somewhere and have nothing else to do. Definitely beats buying a portable DVD-player or an expensive MP3-player when you already have a phone that's capable of both!