Sorry about the lack of responsiveness to your question. I guess not many SME's are tracking IYP based ROI. eerrr, I guess not many SEM are tracking IYP based ROI for SMEs.
We draw a line for example in the level with which we will track a SME ROI. This is for many reasons, many of which are good, new, threads.
As for IYPs, many have trouble sending you an excel file with traffic reporting every 30 days, let alone business intelligence in tracking phone based ROI. Some are simply afraid of the results.
Specific to your question, which is essentially how to track calls, without unique numbers, or god-forbid, asking prospects how they found you...., I would point this conversation in the direction of pay per call.
Infospace is a leading IYP that recently purchased Switchboard. Recently they rolled out their pay per call service. Take a look. Also take a look at what Ingenio and Click4Talk amongst others are doing. The most important aspects of these services are their ability to track phone calls in a robust extranet enviornment with rich features for business intelligence.
This behavior is going be indicative of moves with the leading IYPs in the second half of 2005. Then there is VOIP ~ as communications integration to advertising speed the transition to call tracking, in addition to its applicability to usability and utility for searchers.
The Pay Per Call service structure is an advertiser tool, a tool for the inventory providers, and a brand new compensation model for Internet advertising. It is a significant development and immediately applicable to call tracking.
Finally, have you noticed the trend towards the iconic phone navigation, which requires users to click on a phone icon to view the number? This click, (albeit) perfectly imperfect, is a means to monitor request for phone number. I know, silly, but it is indicative of the fact that many are concerned about the challenge you raise. Thanks.