Custom Adwords Cookie

Need to setup a Cookie session for people if they come from Adwords that would allow us to change the phone numbers listed on the website. We are trying to setup Call Tracking for this site, but they have 10 different numbers listed and so I have established how to implement. But need help to implement. If you go to ecmservice(dot)devplaces(dot)com or ecmservice(dot)devplaces(dot)com/contact-east-coast-mechanical There are 2 key aspects to this project one within the header, there is a change button that changes the number in the header along with the Contact page of the site which has all 10 numbers listed. My thinking is that we can setup from Adwords to come to the website to include some variables such as "/?source=Adwords". When someone comes to the website with this URL, it will trigger cookies to be setup with the unique phone number for each location. If someone comes to the website without this URL in the variable, it will use the default numbers currently listed. And then just have the website changed to show the variable phone based on what was setup within the cookie. FYI: This is the DEV version of the site, so there is no concern for downtime or temporary errors while coding. This site is a Wordpress site.