I like the idea as well but I can imagine that $10/hr employees are not trained/educated/{whatever adjective you pick} enough to do the negotiations. The proof is there: they are working for $10/hr. If they had quality skills like that, they wouldn't be making $10/hr in a call center. This means they would require extensive training (which would up the overall cost, particularly the upfront cost to get started).
Now as to the idea, I think it falls into the, "I'd use that" category from a user perspective and would have a B2C model; in my view of it, you would sell directly to consumers or partner with companies to sell at a discount to their members/userbase.
* How do you bill? Do you bill differently for monthly bills (i.e. utilities, car loans) vs. one-time expenses (i.e. jewelry purchase)?
* Is this an unbiased service or will your company step in at "just the right time" and say, "You can save $100 on car insurance right now with our preferred provider!"
* What is the average amount to be negotiated?
If it is $100/month bill, then you should be able to negotiate down to $85-$89.99/month. That means you save the customer, on average, $12/month in that scenario. How do you convince me, the customer, that your price is worth my saving $12 a month?
* How much did it cost you, the entrepreneur, to save your customer that money? I'd assume it cost a minimum of $7 in raw time on the phone/logging the call and then another $10-$100 in training/software/"misc" costs depending on what they were negotiating.
Anyway, just random thoughts. This is one of those, "Cool idea but I can't figure out how to actually make money with it" ideas to me.