If you are coming from Europe with a GSM telephone, there are only two GSM networks in the USA. They are AT&T and T-Mobile. Of the two, I believe AT&T has the most coverage across the USA. There are many companies that offer prepaid phone service, and I don't know which offer the best prices,. You will have to check each of them to decide which is best. Domestic calls in the USA are rather inexpenisve with rates as low as 2 or 3 cents per minute. Many overseas calls are only 10 or 20 cents per minute.
Another alternative to using a SIM card, is to just buy a disposable telephone. They are available at many drug stores and discount stores for less than $100, and you can purchase prepaid minutes on those telephones.