Do not activate "Face Down to Vibrate Mode," if you do, you won't be able to get ringtones back.
My handset is not set to silent or vibrate, but my handset only vibrates now for incoming calls; I am trying to assign a ringtone to my handset, but it only vibrates.Ring. Ring. Ring.
If you activated either of your smart profile settings "Double tap to silence" or "Face down to vibrate" from the Sound and display settings menu, your audible ringtones might be come disabled and your handset will only vibrate.
This behavior will be corrected in an upcoming software release. If you activated the smart profile and your ringtones are no longer working, you can try this workaround or ultimately, you may will need to perform a factory data reset to clear your handset and restore factory defaut settings back to your phone.
First try a workaround before completing a factory data reset:
Make sure that the "Smart Profile: Face Down" feature is enabled.
Hold the phone face up in your palm.
Call yourself from another phone.
As the phone is vibrating, DO NOT ANSWER.
Still holding the phone, flip the phone face down as it vibrates.
Then, flip the phone back over so that it's facing up.
End the call from the phone you are calling from.
Leave phone face up and call yourself again. If it does not work on first attempt, try steps a few times before resetting the phone.
If the workaround did not restore your ringtone. Scroll down to bottom of FAQ for instructions on Factory Data Reset. The procedure will require you to sign back into Google and set-up your account over again. When your handset is back online, it is recommended to not activate the smart profile again until we have corrected the behavior.
Their factory reset instructions make me realize the Droid X has no backup! iPhone wins, and has ringtones.
Update here on how to fix no ringtone on Droid X.