The Messaging app on the Motorola Droid doesn’t allow you to send somebody a ringtone via text message. There is a workaround for this problem though. It’s quite a few steps, but here’s how.
1. Download and install the Handcent app from the Market.
2. Open Handcent.
3. Start composing your message by tapping the icon in the upper left corner, or tap the contact you wish to send the ringtone to.
4. Press Menu > Attach.
6. Select the ringtone you wish to send, then tap OK.
7. The ringtone will be added to the message, where you can then send it off to its recipient.