As several people have stated, it really varies with where you are. I was all over most of the country in Costa Rica, and several Northern parts of Panama. Since there are really no amphibians left (bar a salamander or two) from Monteverde, that soil won't be a great model-- unless someone here has some Bufo periglenis hiding in their house and need to let them bury for the majority of the year. Most of the Caribean (D. pumilio, P. lugubris, and D. auratus) soil is fairly loose, and has a good deal of leaf litter on top. The Pacific is much drier for part of the year, so tended to be more rocky in the soil. This isn't true for all cases, but for several. The Pacific was where the D. granuliferus, P. vittatus, and D. auratus are found (anyone else see the trend of D. auratus being everywhere...). I would just stick to the soil mix I've always used. Mine is a mix of Michigan Peat moss, milled sphagnum, orchid bark, and play sand. I still think this is one of the better mixes. With a little 'tweaking' I use it for my geckos now as well. The main key is leaf litter in some parts for most frogs, and tons especially for D. pumilio.
Best,
Justin