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.
CrackBerry is in no way Affiliated with BlackBerry. We take pride in our unbiased content, however do occasionally receive free products from vendors that we review or discuss. For more info click here.