This is something that one needs if one calls many people in the allocated 4 hour period!
Yes, an Autodialer. This is also called Ringless Voicemail.
I am sure you know about SlyDial - this product is similar to that.
The good news is how it is priced. However, you may end up paying more if you decide to call many more as the charges are per call - and not monthly.
(I will have to do little more research for the same though.)
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Disclaimer: I have not used the services of this product, yet.