Netimperative reports that Espotting is to launch its pay-per-call service in the UK. Running already for some months in the US, the idea is that the web user clicks on an ad and is then presented with an online ad with telephone number.

Unlike pay per click, however, you only pay if someone calls. An ideal solution for call centres with web sites which are less than effective, you might think.

That's because the downside is your web site doesn't perform its normal role of conversion - and you are totally reliant on the call-caller relationship. This isn't necessarily an issue - but it does mean re-thinking your strategy.