How to have any song as your iPhone ringtone by using GarageBand
However, there is a way to work around this situation right under Apple's nose. You don't have to jailbreak your device or do anything non-legal. You only need to obtain a copy of Apple GarageBand for iOS, which is free on devices that shipped with iOS 8 and costs $5 for everyone else!
Then, you'll have to put the song through GarageBand and turn it into a ringtone through a special procedure that Osas Obaizamomwan from iPhone Hacks clued us in for! Check this out, it's good stuff.
source: iPhone Hacks