Shopping for small business VoIP == flea market?

I have a phone-based business idea I've been trying to implement in the United States revolving around domestic calls.

I'd like to buy a number of 8xx DIDs and buy minutes in a pay-as-you-go arrangement. I'd start with a dozen numbers, doing a few thousand minutes a month, and hope to grow to hundreds of DIDs and bill

I'm definitely going to use Asterisk for the PBX side of things. Clunky and confusing as it can be, Asterisk is worth the pain and can probably do anything, even if I have to write the code myself. I feel secure in my answer there.

But I'm getting increasingly discouraged while trying to set up and use small-fry business-focused VoIP services. The prices are often great, but voice quality and consistency are often erratic, customer service overwhelmed, confused, or simply not available. I get the sense that everyone is oversold and understaffed.

(I can name names if it is required, but really I don't want to badmouth any of the five providers I've tried. I have yet to spend real money with these guys or do much more than experiment. I'm frankly astonished that these guys can make money at all. But I do feel confident that my experiences are typical, even maybe leaning toward the "good" side of the typical experience. It just isn't adequate.)

I'm willing to spent more than $0.02/minute for US domestic calls. I'm willing to spend more than $5/month for an 800 DID. I'd happily double all those figures if it meant I could actually get good quality service. I might well go higher, although at some point the original model breaks down and my idea is no longer profitable.

I do realize going with VoIP does mean reduced quality somewhere. Lag, compression, etc. I would happily accept less than perfect voice quality if I could count on that service being reliable (at that degraded-but-consistent quality level) and available, and with support.

Who are the larger providers all the small-fry are reselling? Would any be willing to deal with me while I'm small, charging accordingly, with price breaks as my volume grew? Who should I be talking to, if anyone?

At what point should I stop looking at VoIP and start looking at TDM? How much is TDM likely to cost me for the figures I quote above?

I do want to do all my own PBX work, by the way -- the business depends on this fine-grained control. The managed VoIP/PBX systems are not for me.

Thanks for any help.

Chuck