said by ThaiGuy:
I am a fan of both CC and voip.ms, so my preference would be to use them if possible. Am I correct in thinking that they use different CLEC's thereby giving me the redundancy I require?
Probably a good idea to use different retail VoIP providers but there is no guarantee that they'll use different CLEC's in any given community (rate centre).
Many CLEC's have merged, reducing the choices.
By the way, it seems that Voip.MS uses Vitelity (also called Sixtel or EXGN) for many/most of their US phone numbers (DID) and also tollfree numbers, but surely they use others too.
Local phone numbers (DID's) are provisioned by Local Exchange Carriers (LEC).
The original LEC in a community---essentially the POTS company---is the Incumbent Local Exchange Carrier (ILEC).
In the majority of the US that was covered by the Bell System pre-1984, the ILEC is often called the Regional Bell Operating Company (RBOC or Baby Bell). Seven RBOC were created after the 1984 government breakup, but after lots of re-mergers we are left with Verizon, a resurrected AT&T, and CenturyLink (as successor to the ill-fated USWest RBOC).
Newer competitors that have entered the market are allowed access to a pool of phone numbers, and are allowed to connect to the national network, because the government mandated it. These are Competitive Local Exchange Carriers or CLEC's.
No type of LEC provides 800-type tollfree numbers, because the L in LEC stands for Local, and these are not local.
Rather, toll-free numbers are in a pool run by an organization called SMS/800 that traces back to the former Bell System and then became jointly owned by the RBOC's.
Only certain companies are allowed to access the pool of TF numbers operated by SMS/800.
Those companies are called Responsible Organisations, hence RespOrgs.
So directly or indirectly, any TF number comes from a RespOrg (pronounced "resborg", not to be confused with Starfleet's team assigned to research the borg).