You already know this so I'm just reminding to test, test, test.
I've done a lot of recorded messages for real estate entrepreneurs. It's basically an audio sales letter. You should consider the same format. The first line in the message is your headline, make it bold. State a problem/ask a question, let them know there's a solution, assure them you have the solution, and ask for their info. Of course be interesting, keep tickling their interest, and close hard.
When I was in retail I learned the number rule is "Never let the customer walk without getting their info." A soft close and not yanking their contact info from their wallet or purse is equivalent to letting them walk. If they called they're already light years ahead of anybody else in the world and your best chance to get a lead and only chance for this particular caller. Don't give up and don't let them walk.
Here's another tip about 800#'s. You'll get hangups, it's inevitable. Since they're calling an 800# on your dime, the feds put into law that you get to see their phone number. Your service should give you a report noting which ones hung up and sometimes their reverse lookup info like their name and city.
Call those numbers back with something like,
"Hello, my name is xxxxx yyyy. You called my 800# on xx/xx/2008 and my phone service notified me that you didn't get to hear my entire message because the line got cutoff. I know the information would be of great value to you so I'd like to get your contact information now and I'll get the package right out to you."
Or whatever it is you're doing for them.
There's a dozen ways to do this including like, "hi, you called, you got cutoff. Oh, it looks like I caught you at a bad time. Let me get your contact info and I'll get that package out today. Did you want me to snail mail it or use fedex?" Endless possibilities. Test, test, test. GL