All they have to do is have an incrementing autodialer. It starts at a prefix, say 235-0000 and increments through 235-9999 before going to the next prefix. Any unlisted numbers in the range get hit just the same and listed ones.

Since Colorado passed the No-Call list, the number of telemarketer calls to my home has dropped dramatically. When the national list became available, all registered Colorado No-Call list people were automatically included.

The downside to this is that several thousand people have lost their telemarketer jobs, including several hundred of them here in Colorado Springs. While I can understand their plight, they don't have a right to bother me at my expense. Just as I have a No Soliciting sign on my front door, I want the same for my phone. Now, if we can only expand it to cover non-commerical (e.g. political) telemarketer calls, that would be another step forward, IMO.