The latest iOS available for the iPhone 4 is iOS 7.1.2. Apple Music application is available for iOS 8.4 or higher, which means you are not able to download and install Apple Music on iPhone 4. Someone may find other music programs to replace Apple Music. Instead, someone sticks to install Apple Music on phones. What they can do to enjoy Apple Music songs on iPhones 4. Rather than taking a risk to upgrade iOS 8.4 on iPhone 4, it would be better to see if there is a program to help you unlock Apple Music from DRM protection. To be honest, the latter solution comes easier.
Why I say people need to do DRM removal from the purchased music from Apple Music app. Because Apple Music is in encrypted M4P format, only you bypass the limitation of Apple's Fairplay, then you can transfer them to whatever devices, like, iPhone 4, iPod Nano, iPod Classic or stream them to any online sharing channels you want, like Roku, Chromebook. What tool will I recommend to convert M4P to plain MP3/ M4A is Apple Music Converter.
iPhone 4 support audio format
AAC (Bitrates 8 to 320 Kbps)
Protected AAC (used for DRM copy protection on the iTunes Store)
ALAC (Apple Lossless)
MP3 (bitrates 8 to 320 Kbps)
MP3 VBR (Variable Bitrate)
AA (Audible formats 2, 3, 4) / Audible Enhanced Audio / AAX / AAX+
Step by Step to Convert Apple Music to iPhone 4
I will recommend you to use Apple Music Converter. This is a good tool to convert Apple Music or iTunes playlists to lossless FLAC or AIFF so that you can enjoy them in CD quality freely. Moreover, after you convert them, you can keep them forever after the end of subscription by converting them to MP3. You can specifically set the bitrate, sample rate and codec.
Step 1. Install the Program
Install Apple Music Converter on your PC and launch it. Make sure iTunes is closed before launching the program. Then iTunes playlists will be synced to the converter at in few seconds. You have no need to import files manually.
Step 2. Select MP3 as Output Format
Choose Apple Music files you like to convert by checking the optional box next to music tracks. Then go to the bottom of interface for more output settings. Click "Output Format" > press drop-down arrow > select "MP3" from the format list.
Step 3. Start Converting Apple Music
When you are prepared, you can press "Convert" button at the top menu bar to run the conversion. Batch Apple Music conversion is also allowed.
After you convert Apple Music to plain format, you can free to listen to Apple Music on your iPhone 4 or anywhere. Apple Music Converter provides you a stable and secure conversion process, so have a try on it!