In the old days, if your law office wanted to take credit cards, you would probably have to sign a years-long agreement with a credit card processor and pay exorbitant fees on each transaction. Heck, in even older days, you would have had to use one of those heavy metal machines that used carbon paper. (True story: I saw one of those in use at a restaurant the other day.)
Today? You can take payments online. You can use a reader the size of a nickel that plugs into your smartphone. Or if you're feeling super adventurous, you can try something really new, like Apple Pay or one of the other NFC (tap-your-phone) readers.
Here are a few options, from slightly more old-school to bleeding edge: