My wife has one of each of these phones. I wondered if she could have snippets of her favourite songs as ringtones? what exactly can be stored on the SD card?
On your Doro 6520, go to Menu -> Settings -> Sound -> Tone setup -> Ringtone -> Ringtone -> User to select from your downloaded ringtones. As for Doro Primo 805, you can't use downloaded ringtones. Hope that helps.