Over the course of the last year, Google’s AdWords advertising platform started launching a number of new products that allow advertisers to link ads and phone calls. Those include click-to-call ads, call metrics and calls as conversion in your AdWords stats, but today, it is taking this concept a bit further with the launch of Website Call Conversions.

Here is how they work. You set up your regular search ads, but every time somebody clicks on them and lands on your site, they will see a dynamically generated phone number that is linked to those ads. When potential customers then click on the number or dial it directly from their phones, the call will automatically be linked to the original ad the customer saw and you can more easily track which ads drive phone calls.

Until now, it was surprisingly hard to link incoming phone calls to ads. Google cites 1000bulbs.com (“Looking for a great online deal on light bulbs, halogens, batteries, light fixtures or other lighting products?”), which beta tested these new dynamic phone numbers, as an early success story for this service. “After implementing website call conversions, we discovered that AdWords was not only driving over twice as many calls than previously thought, but that our customers also talk to us for over five minutes on calls originating from our site,” says the company’s director of marketing Jeremy Foster. “Insights like these are helping shape our web strategy and the way we serve our customers.”

Based on the conversion data, advertisers can then optimize their ads and bids to drive calls that are more likely to generate sales leads, for example.

To enable this feature, advertisers only have to add a small code snippet on their desktop and mobile sites. The design of the numbers can be styled according to the advertiser’s website’s branding, and numbers stay active for 90 days.

The only problem I see here is that many potential customers may want to call you back a few months later. If they saved the number they found on your site and that Google forwarding number isn’t active anymore — or was recycled and now points to a completely different business — there’s quite a bit of potential for confusion here. I asked Google for clarification about this and will update this post once I hear more.

Update: I just heard back from Google and the initial numbers will continue to work even after the 90-day period.

The service is now available in the US, UK, Germany, France, Spain and Australia.