This is a relatively new tactic because it started appearing in the past decade or two, thanks to the novel marketing opportunities provided by the internet. Using a toll-free number that is either your domain name or a domain that is your telephone number are fine (and clever) ideas. For example, if you decided to use 1-800-COOKIES, why not also use 1800COOKIES.COM to carry the branding through? This will not only make it easier for the consumer to remember your telephone number, but you will see increased traffic to your website because consumers will be able to more easily recall your domain name as well.
There is a trick that will make the process of getting a domain name that doubles as your toll-free number a lot less stressful. Choose the toll-free number first. If you get the domain name first, you run the risk of your toll-free number being taken, despite the fact that you already have a domain name that clearly markets that phone number. Why take the chance of sending business to a competitor who already snagged your ideal toll-free number by having a domain name that includes their toll-free number? This is yet another reason to get your toll-free number as soon as possible. Avoid having your perfect number bought up before you have a chance to grab it.