Hi Ingrid,
I tend to be very hands on about the way things get done in my business and I can't even imagine having someone else follow up with my potential clients - there's no one who can answer questions, give a good perspective into the company philosophy and energy, etc. like me....
I would also suggest that unless you're considering starting a team of VAs (with the person you hire to call for you as part of it) it might be a bit off-putting to potential clients to realize that the person they're speaking with is not the person they'll be contracting. It may leave them wondering if they did contract with you, would you be outsourcing their work to other people as well?
I doubt that anyone you hire to call on your behalf could answer any inquiries with the same knowledge, expertise, and enthusiasm that you can.
It may be a big time investment to make these calls yourself, but when you consider the payoffs of taking that time it's surely well worth it. If the list is really massive, then send it out in batches and follow up in batches. No sense in overwhelming yourself all at once and that way you have complete control of all communications with these valuable potential clients.