If it's your device and you have access to it to install software, take a look at GPSed and Trackem. Both will do what you want. You can find links to them in the GPS & Mapping Forum. Some carriers have similar software. Verizon's is called Chaperone 2.0. According to the press release (I haven't tried it yet) it can track multiple devices simultaneously. Since your aren't sure what the device is, it makes me suspect you are trying to track someone else's phone. I can't help you with that.
If for some weird reason you're trying to locate someone else, it requires setup from the phone. In short, you have to have possession of the phone to set it up.
