This seems like a pretty decent storyline idea, and like a lot of other people here, I think a lot of it is gonna depend on the quality of the writing.
One thing I'm not too sure about is the ending part...like what happens after he dials the number. Reading it, it seems like the actual Earth, with everyone in it becomes taken over by Hell, and then by the end, after Satan is defeated, the entire world turns to religion? I'm not really sure if I like that, just because it seems a little too broad and epic for me...
An alternative, just off the top of my head, would be maybe having something like Bryan becomes a changed man after all this happens, and accepts religion into his life, without it neccessarily being an event that affected the entire world, you know? Like maybe have him win, then it flashes back to the hobo standing in front of him at the church, but instead of asking him for change, the hobo just keeps on walking (so it's like all of this happened as a 'what if?', and Bryan ends up back at the exact moment that he made that initial decision). You can still have the hobo be God, and then it is more of a re-familiarizing-people-with-religion-on-a-personal-basis kind of thing. Maybe even have it end with another person being approached by the hobo, and once again being asked if they beleive in god?
Definately keep us ut-to-date on how this goes, because it seems rather interesting.
On a side note, in third semsester, i took an advanced script writing course and came up with a script that I am so proud of...it takes place in the First World War, and without going into TOO much detail, involves a medieval undead army rising up on the battlefield between the trenches, slaughtering most of the German and English soldiers in their respective trenches, causing the survivors to join together to survive and defeat the undead. I actually based it on the story of that Christmas day in WWI, where both sides came up from their trenches and palyed football/soccer together.
The story may sound a bit stupid, but don't worry (because I know that you all are...), I actually researched stuff and found a place that was the site of bth medieval AND WWI battles, and the first act pretty much details the medival side of the story, and how the general was betrayed and so his army rises every 100 years...blah-blah-blah.
All-in-all, I just wanted to write about skeletons, wearing armor, carrying axes, riding their skeleton horses, and being shot at by German and English WWI soldiers, because, damnit, there isn't enough of that shit going down these days.
Anyways, sorry about the long tangent, I am tired...so...yeah, veg, what I said in the first half.
EDIT: Forgot to add my name!
Dyko (that's the stuff...)