Cellphone signal boosters are typically static, expensive, bulky things; Cellranger is an attempt at getting this class of device into the pocket (or at least the rucksack) and hooking it up to mobile power sources such as cigarette lighters and USB.
It doesn't need to be attached to the target device: it passively boosts whatever it gets to the immediate surroundings.
My experience of such devices is that they work as ways to push signals into dead-zones. You'll still be limited to whatever download speeds and call quality you get in your general location, but you can now bounce them into that 6ft lead-lined sarcophagus you're using as a office. Given its short range, it's worth bearing in mind that it won't help the uplink from your phone to the tower.
To be launched on May 28, the Cellranger is GSM-only and will cost $150.
Product Page [Getcellranger. Thanks, ministryoftruth5!]