I have ringtones that were from my blackberry. They're mp3 ringtones that I made myself and such. How do I put it so I can use them as a ringtone on my iPhone 4G?

PLEASE don't put any responses that lead to websites to download free ringtones. I don't need that, I have the ringtones already made and just need to have it be used as an actual ringtone option for my iPhone