Is it possible to detect if my visitors are coming to my website via a Google Adwords Ad?It would like to change the telephone number for those users only, that way I can measure the success of my adwords campaign with the number of calls. 
Javascript - Detect if user is coming from a Google Adwords ad
javascript;google;google adwords
You can use the special utm_ query string parameters mentioned here:http://adwords.google.com/support/aw/bin/answer.py?hl=en&answer=156114Then switch your phone number out based on (for example) utm_campaignIf you use the auto tagging feature (on by default) the parameter to look for is gclid:http://adwords.google.com/support/aw/bin/answer.py?hl=en&answer=55596