Google has just launched "Bid-Per-Call" on adwords which allows advertisers to pay per inbound call that comes in. http://adwords.blogspot.com/2011/10/introducing-bid-per-call-in-adwords.html This can be very powerful and can be part of a strong lead generation strategy. I think it is especially useful for local businesses and can be very effective when targeting the right locations and niches.
They give you a new toll-free number with which to track your calls. It's a great service and I'm happy to hear it's back. It worked great for me at my previous company.