I am interested in using the number theory library (NTL) for developing C++ Android software, but I don't believe NTL is supported by NDK. What could I do so I can use NTL?

If the source for the library is available, then you could place the soruce in with your native code and compile it into the same library.

Thanks for the idea. I tried doing that but the NTL Library has dependencies such as iostream which for some reason doesn't appear to be supported by NTL. Is there a suggestion on how to deal with this?

Thanks.

look here:
http://smartctl.net/android/ndk-r4.php

It's a modified version fo teh NDK that has support for the full STL library (including iostream).