Make it paid, and you might have a fighting chance with executives and salespeople. Executives get cold-called AND cold-emailed by terrible salespeople all the time. Know why? Both media are essentially free. Paying would create a much-needed quality barrier in these irreplaceable but miserable media. Free isn't always better...how are you planning to make money anyway?
The registered email address getting the redirection to it's own phone pays for that service by the minute... at a rate comparable to SkypeOut. This is TollFree at really great rate.
Oh, did I mention, once you have an account, you can also dial out to normal phone number using simple URLs again... and pay for that. But this is really an add-on.