One thing I appreciate the most in travel is the large buttons, particularly the volume buttons that the designers conveniently placed on the inner lip of the right earcup, so they're easily found by touch. You shouldn't have to fumble around or remove the headphones to raise and lower volume or answer and end calls, and yes, there's a built-in microphone. Of course, if you're using a smartphone to stream audio, you'll most likely use the virtual buttons on the device rather than the hard buttons on the headphone to control audio playback.
As with most other Bluetooth headphones I've encountered, pairing your smartphone, tablet, or other Bluetooth-enabled device with these guys is easy enough, though you'll run into an occasional snafu from time to time. Also, expect to have some dropouts now and again; that's par for the course for Bluetooth, which has a range of about 30 feet.
Performance, as I said earlier, is very good and arguably the WP-350's strongest point. In going wireless with Bluetooth headphones, you usually have to give up some sound quality because Bluetooth compresses your music and has a tendency to flatten out fidelity. You'll experience some of that with these headphones, but the sound quality holds up well against that of comparably priced wired headphones.
The WP-350s offer decent clarity and deliver a good amount of bass. They also play loud and work pretty well with all types of music. These are by no means audiophile-grade headphones, but I thought they sounded better than a lot of in-ear Bluetooth headphones I've tested, and delivered almost as good sound quality as the pricier AKG K830BTs (also an on-ear model), which cost significantly more and aren't as comfortable to wear. I also thought they were superior to a pair of JayBird Wireless SB2TR Sportsband Bluetooth headphones I had in-house.
As far as using the WP-350 as a headset for making calls, it's only fair. You can hear callers quite well but because the microphone is housed in the right earcup, it's a little far from your mouth. My test callers said my voice sounded a little muddy and slightly muffled. They could hear me, but I just didn't come across totally clearly.
Finally, battery life is rated at 8 hours on a single charge, which is a standard spec for Bluetooth headsets. I was able to use them for a full week on my daily commute without having to recharge, and I travel a little less than 2 hours a day.
Creative's WP-350 Bluetooth headphones won't blow you away with their design or comfort level, but their performance in those departments is capable enough to justify the affordable $70 price.