Is it possible to use airdrop on iphone4?
No, you can't use Airdrop with an iPhone 4: http://support.apple.com/kb/ht5887

While your iPad mini supports AirDrop, the your iPhone 4 does not - and as far as I'm aware, music can't be transferred via AirDrop.

That said, for $25/year, you can turn on iTunes Match, which will put a copy of your iTunes library in iCloud, allowing you to access your music anywhere. You can also transfer the music by using a Mac.