I actually have a little support for this idea, but only a little. Firstly, new characters should need to hit level 10 to access whispers across the board, but allow new players below that level to send tells to their friends only. Honestly, at low levels you rarely use tells anyway, since it's a largely solo affair.

It won't affect anyone who's been playing the game long enough to unlock job changes, but it will at least stop gil-spammers from deleting characters and remaking them to avoid detection.