You already know that you can create music playlists using iTunes on your Mac. Well, when you're away from your Mac and you have inspiration or desire, you can create playlists on-the-go on your iPhone, too.
iOS 4 lets you create playlists.
With iPhone iOS 4 installed on your iPhone 4 (or iPhone 3GS or 3G), you can create playlists with the music you have on your phone.
Create a playlist.
Launch the iPod app, then tap the Playlists icon in the lower left of the screen. At the top of the list of playlists you'll see "Add Playlist..." Tap it and name the New Playlist as you like.
Choose your music.
Now, choose music for your playlist by tapping songs. You can search for songs using the search field or by browser your music genre, artist and other groupings.
Tap done to save the playlist. You can add or delete music from this playlilst by selecting it and tapping Edit.
Playlists you create on your iPhone are just like the ones you create in iTunes on your Mac. All playlists you create on your iPhone will be copied over to your Mac the next time you sync your phone.