The cylinder-shaped headset itself is relatively small, measuring just 2 inches long and weighing 0.3 ounce. The compact size and the absence of a boom mic make for a subtle style, and we liked the simple silver-and-black color scheme. Like the Tekkeon EzTalker Mini, the Discovery 640 fits directly in either ear via a rubberized ear gel and can be worn with or without the ear hook. The headset slips on and off with ease, and you get three sizes of ear gels, so you should get a comfortable and secure fit in almost any ear. In fact, the fit was so secure that we preferred not using the stiff, uncomfortable ear hook at all.
Controls on the Discovery 640 consist of a volume rocker/mute button and a call-control button, which you use to place and end calls, power the headset on, and ready it for pairing. Though rather small due to the headset's size, the controls were easy to find and manipulate during a call. The Discovery 640 also has a ring-shaped LED light that flashes during charging and when the headset is in use.
Now on to the 640's main attraction: the collection of mysterious silver tubes. The first tube functions not just as a charging base but also as a carrying case. To power the headset, you slip it inside the base and attach the compact wall charger to the bottom. Though we normally don't like headsets that need a charging base, the whole setup is so small that we didn't mind at all this time. As a carrying case, it also comes with a clip for attaching to a pocket or a belt. Be warned, however, that the headset does not snap in to the case very securely. When turned upside down, it fell out of the case more than once.
Plantronics wisely included two other charging options with the road warrior and the commuter in mind. First, if your battery is low and you're away from a wall charger, you can charge the headset with a AAA battery. The battery fits into a cylindrical holder that attaches to the end of the charging base. When attached, the two parts are no bigger than a Magic Marker, so you can easily stash it in a front shirt pocket. A battery comes in the box, and Plantronics promises that one battery will charge the headset two full times. Lest you think that's all, the 640 has one more charging option. Taking advantage of the fact that travelers will already be carrying around their phone charger, Plantronics provides four adapters that can mate with chargers from most Nokia, Sony Ericsson, Siemens, and Motorola phones (other models are not supported at this time). Like the battery tube, the adapters plug in to the bottom of the carrying case. And because they're less than an inch long, they barely take up any room. There's also no reason to worry about how to carry around the entire headset kit; nearly all the parts aside from the wall charger fit into an attractive brushed-silver case.
We tested the Plantronics Discovery 640 with the Sony Ericsson S710a. The pairing process was easy to understand, and we were up and running after only one attempt. Audio quality was very good, with plenty of volume and little static. Voices occasionally sounded a bit hollow, but callers said they could hear us quite clearly. In fact, one caller said he noticed an improvement over a wired headset. In windy conditions, call quality diminished somewhat, but it was nothing we couldn't stand. Call features include last-number redial and voice dialing. The 640 has a rated talk time of 5 hours with the normal charger and up to 15 hours using the AAA battery. The rated standby time is slightly less than three days.