Do a little better at validating US phone numbers

Some area codes/combinations are invalid; adding this regex to catch a few of them. See http://stackoverflow.com/questions/123559/a-comprehensive-regex-for-phone-number-validation, and also http://stackoverflow.com/a/11018836/175689 ... there is probably a more bulletproof solution but this is an improvement.
Prevent saving an invalid phone number on a contact

Wasn't actually checking validation of phone number in UI. Not writing any more tests until we combine contact & phone number.