Leaf curling is quite a common complaint on tomatoes and there are many causes including environmental stresses and transplant shock. Some varieties even curl their leaves naturally!
Do you know whether the tomato plants had been hardened off before you were given them? If you have put them straight outside then the sudden exposure to the elements and change in temperature may be the cause. Leaf rolling is also often associated with tomato plants that have been over watered, or experienced periods of heavy rainfall. Tomatoes need to be kept reliably moist without becoming too wet or too dry. Quite often, leaf rolling is a temporary response and the plants will improve once their environment improves.