Hi there,
I have a m500 too that I got recently. It's been a long, hard road for me to find a way get a custom ringtone onto the phone through the data cable. I actually found this thread while Googling in vain for the answer. So I've figured out that I needed to convert mp3 to 3g2 and then set it to video ringer. So after that was done, I noticed the same problem as you TheSupernova. Since after a powercycle, I noticed that it played my tune set for Without Caller ID, I figured that both must be set to Video Ringer. So I did that and what do you know, it works!
So the conclusion is that for Video Ringer to save after a powercyle, you must have
both With and Without Caller ID set to video ringer. I signed up for these forums just to tell you and everyone this little tidbit because I know it was really annoying for me and this problem hasn't come up anywhere else when Googling.
Hope that helps!
