I have been buying tracks on iTunes for many, many years now. I noticed that not all of my music had followed me between new computers, new iPods, new iPhones, etc. Here’s how to get all your old tracks back that you’ve purchased from the iTunes store. Note: This is being done on an iPhone 4s, but was tested on a 4 as well. I have not tested it on a 3 or 3s, but I assume it’s more relevant to have the iOS5 update.
Open the itunes store and click the “Purchased” icon
Press the button for “Not On This iPhone” and select an artist
Once you have selected an artist, it will display all the albums by that artist that you have previously purchased from. You can opt to download all songs on a particular album by pressing the cloud icon, or choose “All Songs”
Here, you can either download the entire album or choose individual songs. Press the cloud icon and it will place that item in your download queue. Presto! You now have access to ALL your previous iTunes purchases!