I brought down a shelf by issuing an incorrectly formatted dial string before. Evidently dialing "w5551212" wasn't possible, and it really didn't like the idea. They have since updated their software version.
Usually we just get throttled, which is frustrating, because you get a normal return as a busy. When you call the LEC/CLEC all you get is "well the circuit is showing up". We have had to implement dialing rate controls in order to make it more CO friendly. What we have found is that calling around 10 calls per second is sustainable usually. Anything higher then that and you run a pretty good chance of the provider freaking out. Other issue is call surge. There is a surge in dialing every 2-3 seconds (waiting for ringtime on placed calls). That means that on a machine with 8 T1's in it, assuming this is a 5:1 dialing campaign, that every 2-3 seconds about 150 calls are beling placed ((8*23/5)*4). These 150 calls are in theory spread back out over 8 T1's, which gives a dial rate of around 18 calls per T1 every 2-3 seconds. That's a lot of dialing for most providers.
SIP Providers usually have even less capacity
