You would need to know the carrier. You can send email messages to
![[email address]](http://www.blackberryforums.com/?emailimage=fd789d35266543b2398d6431f92fad62)
, but I have had problems with that here (specifically Alltel and Cellular One would get messages back saying that they could not be delivered).
If you go to
http://fonefinder.net, you can look up the prefix and area code, and get the provider (as long as they have not ported their number elsewhere)