PSTN provider recommendations?

I’m looking for a new, US-based PSTN provider who supports IAX and has a lot of available DIDs in a lot of NPAs. (Am I over my acronyms per post limit yet?)

I’m researching the idea of starting a niche VoIP provider service and the PSTN provider that I’ve currently been testing my setup with (Voicepulse) is really beginning to disappoint me.

I have used and recommend them.