Will iPhone 4 factory reset delete my music?

I want to factory reset my iPhone 4 because its awfully slow but want to know if that will cause my music i downloaded to get erased! The music is from an application not iTunes.

Note Performing a hard reset is only recommended when the existing data has been backed up or is unwanted. For assistance refer to Apple article: # HT1766 - iPhone and iPod touch: About backups.

http://support.verizonwireless.com/support/devices/knowledge_base.html/39607

Conclusion: it might not, but you should back it up just in case something goes wrong.

Well yea. No matter how the music got on the iPhone it will be erased, along with anything else via a factory reset. Of course it can be put back on through iTunes as well.