||It is logical to use your company name for your domain name if you already have a large market audience. There's no point in a company like Woolworths using a different domain name. Though B&Q stuck with not being able to have the "&" sign in a domain name struck gold with www.diy.com.
But if you are a new business, or new to the internet, or your existing customers are unlikely to be searching for you, then having a domain name that utilises your key words will work better for you.
Not only does mobile-phones.com look more relevant than jsampsonandsons.com to potential visitors when they see them in the search results. But it's easier to remember when recommending your site to a friend, and more importantly most of the search engines will pick up on that keyword relevance too.
Don't be afraid to have dashes in the domain name. www.newmarket-transformers.co.uk have ranked exceptionally well for years. And this is even a benefit in some directories, as they can distinguish between the two words, where they may not with all the words strung together.
If you are J Sampson & Sons, and sell mobile phones, consider buying something like mobile-phones.com for use with the website and promote this. Yet also purchase jsampsonandsons.com or .co.uk for those who already know you, and either have it redirect, or a small site created and hosted for it.