Telemarketing software?

What exists out there in terms of telemarketing software? Any software out there able to automatically leave pre-recorded voicemails to a list of phone numbers?

You could look into robocalling. Specifically...phonedialerpro.com.
I've used their Excel dialer with Skype ($3.99 / mo for a number) and it can leave messages.

Be aware that the effectiveness of this in the US is low.

What I used to do when starting companies was go and use open source programs. Sourceforge has so many things you can use from autodialers to VOIP setups and routing.

For leaving messages, setup a vicidial box. Shouldn't cost more than a few hundred dollars, and depending on the amount of RAM you have you can make 50+ concurrent calls.

If you're actually sitting there dialing and want something to 'click to dial' and track call backs, etc, checkout VanillaSoft, particularly if you're doing B2B calls.

This is all very interesting. It may not be something I can do because convincing my boss to pay anything is impossible lol. Is there any software that can
1. Mask the caller ID
2. ONLY leave voicemail

It would be great to call a bunch of numbers (and not give out our information), detect for voicemail, and THEN leave a message so that it sounds natural. And if someone picks up, stay silent.