Although there is no way of telling 100%, the call pretty clearly appears to be from someone trying a "Borat"-style attack on teabaggers, not an actual teabagger.
Several clear (to me at least) giveaways:
1) The caller says he's from a "small tea bag group." I believe most tea party / teabaggers avoid using the "tea bag" term when referring to themselves. Not to be obscene, but "small tea bag" has a double meaning that is a pretty clear indication this is a prank.
2) The caller seems very interesting in getting Republican Sen. Barrasso to say he was praying for Sen. Byrd to die. This looks like an attempt to catch a Republican Senator in a grisly faux pas, not a genuine expression of concern.
3) The point of the call is that the caller is worried (crying even!) that his prayers for the death of one guy he dislikes accidentally hit a guy he likes. How many genuinely religious people would think that way? Obviously there are certain religious folks who believe God would try to kill their enemies, but how many would believe that God could "miss" and hit a someone they like? I mean, c'mon!
I have to say each of these points are pretty suggestive of fakery, though in different ways. I'm not totally convinced on Point 1, because quite a few Tea Partiers find their way into "tea bag" references or just use the phrase in general. Remember, it wasn't mocking Dems who started using the phrase. Still it's a suggestive point. Two, for my money, may be the best example of fakery, since, yeah, the purported Tea Partier does seem to want to goad Barraso into a discussion of how hard he prayed for Byrd's demise.
But again, what do you think?