As long as you can fit a Sphere of Annihilation into a Bag of Holding without touching it (and costing you your Bag), could you put the Sphere into the extradimensional space of a Bag of Holding and carry it around as your mobile disposing device/magic murder bag/orphan pickpocket deterrent/whatever? Or is this not possible?
A bag of holding can hold a sphere of annihilation...
- if the DM rules the extradimensional space accessed by a bag of holding is fixed (i.e. once an item's in the bag the item doesn't move when the bag's moved), and...
- if the sphere of annihilation's 2-ft. diameter can be manipulated to such a size as to fit in the bag (or the opening of the 2-ft.-×-4-ft. bag can be increased), and...
- if the sphere can be navigated into the bag via the necessary control check.
The first part's easily determined--toss an item into the bag, look in bag, note item's location in the bag, close bag, shake bag, look in bag again; if the item's moved, don't try to put the sphere in the bag!
The second part might require a custom-made bag of holding. The third part's just a d20 + the attempted controller's level + his Intelligence modifier versus DC 30 each round until it's in the bag. Good luck with that.
Please, when you try this at the gaming table, either get a summoned monster to do the control checks or stay the maximum distance away you can from the sphere. Chances are the DM won't tell you what'll happen before you try this kind of stuff.
I have tested this with 3 DMs. In each case I acquired a bag of holding type IV and stuck a rock in. In the case of DM#2, the only case which got past that point, I also hunted down a sphere of annihilation and one of those talisman things. The results:
DM 1: (on step #1, where you look in the bag) "No." (me) "What happens? Is the rock still there?" (him) "Just no. We're not doing this. Moving on."
DM 2: (on the last step, and also every other step except step one, which he rolled for) "Does that work?" (me) "Uh, I think so. I'm not sure though, that's part of why I'm trying this." (him)"Oh. Uh... [discussion of reasons to allow and disallow it]" (him again) "Yah, ok, you can do that."
DM3: (step 1 again) The item moved.