I work for Verizon. FiOS is available in NY, CT, MA, NJ, PA, DE, MD, VA (their original NYNEX/Bell Atlantic "East" territory), and in FL, TX, CA, RI, SC, WA, OR and IN (their original GTE "West" territory). Note that FiOS TV is not currently available in CT, SC or WA, but FiOS Internet is.
More interesting to most than the 50/20 speed will be that on 6/22 Vz increased the 5/2 base speeds to 10/2 in all states that were not already at 10/2 (MA, PA, DE, MD, VA, TX, CA, RI, SC, WA, OR, IN). We also increased our 15/2 speed to 20/5 (PA, DE, MD, VA, TX, CA, RI, SC, WA, OR, IN) And we increased our 15/15 speed to 20/20 (PA, DE, MD, VA, FL, TX, CA, SC, WA, OR, IN).
These are the speeds that new customers will get. If you're an existing customer, you'll need to contact Vz, and possibly renew/renegotiate your term/contract.