After complaining about receiving only 500 miles for joining, I received the following reply from Frontier:
We are working on getting all the new accounts updated with the correct amount of bonus miles. All of the bonus miles for signing up for an Early Returns account should be entered by the end of next week. (January 15th 2010) There was an error in the system, which cause all of these accounts to only post 500 miles instead of the 1,500 promotion. We thank you for your patience while we get all the new accounts updated.