I don't know if this is true for other phones are not, but ringtones can be a pain in the rear at first with the Bionic until you realize that it's a two-step (or part, as the case may be) process.
As I noted in my first post, for every ringtone you want to add to your phone, you'll have to do these steps:
Navigate to the ringtone on your SD card that you want to use, i.e.,
ringtone A, B, whatever its name is (it will probably start playing automatically; just press the stop button if you don't
want to listen to it)
Press the menu button
Press 'use as ringtone'
That ringtone then gets added to your phone's list of ringtones. You can then use it to assign to contacts or for the phone's ringtone. You have to follow those steps for every ringtone you want added, unfortunately. If there's a way around it, I haven't found it.
Another irritating thing is that whichever ringtone you add last based on these steps becomes your phone's ringtone, so if that's not what you want, you'll have to reset it (menu, settings, sound, phone ringtone, choose from selection).
Now, you can follow the steps you were using in your last post, i.e.,
Navigate to Contacts
Select specific contact
Press menu button
Choose from selection; the ringtone(s) should now be in the list
New ringtone name should be shown under 'ringtone'
Hope this helps.