An article in today's Wall Street Journal (B1) discusses the growing trend, mostly among businesses, to take advantage of ability of VoIP to offer a choice of area codes. Area codes like 212 and 415 (New York and San Francisco) are very popular.
Some businesses are doing it to take advantage of the having a prestige area code. That's of limited value over the long term; as more businesses do it, your area code will have less and less meaning. But another reason some businesses are doing it is to give their customers a local phone number. If you had significant business in the San Francisco area, it is just good business to give customers a local phone number to call for service and sales.
Over the long term, area codes will become less and less meaningful as VoIP spreads and phone numbers become truly portable. What's even more likely is that phone numbers will disappear completely; VoIP actually maps phone numbers to an IP address, meaning that the phone number is just an extra and unnecessary step. Over time, IP addresses will be used instead of phone numbers.