reply to PX Eliezer
Re: By the numbers. If a 7-digit dialling is permissible, or you have the "grandfathered" NPA in a 10/11-digit dialling where no single respectable business has the new NPA yet, then +1 (NPA) NXX-XXXX; otherwise, +1-NPA-NXX-XXXX.
Also, I suggest getting a mnemonic number, and still writing it within the rules such as +1-NPA-NXX-XXXX; for example, +1-800-ASK-USPS (I have a local number similar to that), or +1-800-ITS-UNIX (but using someone's trademark can get you into a big lawsuit!).
It gets more difficult if you don't follow the pairing, though; I'd be careful about getting mnemonic between the boundaries; and I think it's a big no-no to have a mnemonic word overlap between the area code and the local number, unless it's a really long word and you don't expect to be getting any local calls anyways.