I tried to help with this about a year ago, but there was no reply.
Depending on the specific cause, you may have the same issue with a new provider.
Though I don’t use them personally, I agree with @sorvani on Skyetel – their reliability record is outstanding. However, unless you are in one of a few big cities, the CLEC likely has only a single interconnect point with the PSTN and one fiber cut caused by an errant backhoe will put you down. You can avoid this with a toll-free number, which can be routed by multiple carriers, or getting a geographic number e.g. in New York.
Also, if your site does not have redundant power and internet, those outages will likely be more frequent than the provider’s (though in that case, the provider can forward calls to your mobile, etc.)