One of the more attention grabbing iPhone tweaks is a custom boot sound that plays every time the device is turned on, rebooted or after a respring. iOS 7 users with jailbroken devices can grab BootSound for free, and choose from a selection of OS boot sounds. A personalized sound file can also be played.
Once installed from Cydia, BootSound can be accessed under Settings -> BootSound. Default OS boot sounds included with the free tweak are MacOS, Ubuntu, Vista and WinXP. There's also a switch to disable the tweak entirely. Once the boot sound is selected tap the Respring button to enable the change. You will hear the sound when the lock screen appears after starting the iPhone.
One of the interesting features of BootSound is that any sound can be installed. This means the sky is the limit when it comes to creating a personalized boot sound. The file to be used must be in mp3 format. Just put the files in /var/mobile/Library/BootSound and they will appear in the Settings -> BootSound list. Files can be installed in this directory using SSH or with an application such as iFile.
BootSound is available from Cydia on the ModMyi repo for free. Check here for instructions on how to jailbreak iOS 7.x with evasi0n 7. You can also find out how to purchase and install Cydia tweaks with this guide.