To the best of my knowledge only iPhones can be tethered to an iPad for data (with possible exceptions below). Since they can also be tethered via Wi-Fi, and it's faster, I've never been able to figure out why the option exists; unless it's some kind of backwards compatibility with older iPhones that can not generate a hotspot.
Any phone that can create a wi-fi hotspot will (probably) work with the iPad.
It may be possible to bluetooth tether some other phones, but it requires a jailbreak if so. I know there is a jailbreak method for Blackberries (don't know if it's bluetooth). However my knowledge is very limited on that subject. I recommend you go tot he Hacking forum, read all the stickies (a tab in the iPad app, highlighted at the top of the list of threads on the webpage), search for your phone, and then if you still don't' have an answer, ask.
Good luck,.