I've solved this and more with www.getvolta.com. We are a lightweight CRM for companies that rely on the phone.
Our outbound stuff is more advanced, but our inbound is simple. Simply change the phone number on your site with a bit of javascript and you're done. That javascript rotates through a bunch of your phone numbers that we give you, tracks referrers, search queries, etc.
When the phone rings you can have a callerid screen that instantly displays all the above plus history of conversations with that person.
We also allow the person who answered the phone to enter a numeric value after each call. Then, you can see ROI for all the various marketing efforts.
Contact me privately if you're interested in learning more. We are still private, but opening up very soon.
