Spotties and BTF are are a great combination to keep together.
They naturally occur in the same areas and can happily co habitate
The BTF's as tree frogs will hang around the top of the tank mostly, and the spotties at the bottom as they are land dwelling frogs, although spotties have been known to climb given the oppertunity.
The only thing that you should be aware of is that they need to be roughly the same size, otherwise one might eat the other,
Unfortunatly due to an escape i lost my BTF male late last year and therefore have no BTF for sale. (but I have a female full of eggs


)
The only place i know that has some is a pet store but they want $20each - if your intersted pm me and i can arrange to freight them to you but hopefully you can find them cheaper somewhere closer to you.
Sarah