Time Zones Information

Dear Sir/Madam: Information systems department of our company (Seabury&Smith) is involved in building a marketing Data Warehouse. We store information on address and phone for all our customers. Part of this information is the Time Zone. We have to be able to uniquely identify the Time Zone based on the area code or address (state, city, or county ). Also, it's important to be able to identify the correct Time Zone for sates and Area Codes that cross Time Zones (for example, North Dakota). Could you, please, provide help to us regarding this matter. Thank you.