[Original Article: 10.6: Trim Music Files in QuickTime X • comment by: Noelle]
Got it! Trimmed the song for my phone!
– Open ITunes
– right click on song and select “Get Info”
– Select “Options” tab
– Select start time and end time
– Click OK
– right click on song and select “Create AAC version”
And it makes a copy. You can then copy that onto your phone (that is connected to your puter).
This was done using a MAC OS v10.8.5 …

Source: Mac OSX Hints