We're pretty impressed with the Spotify iPhone app but unlike its Android equivalent, it can't play music while you do other things. Close the Spotify app and your music stops. But there is a way around that…
1 First you need to jailbreak your iPhone
Jailbreaking your iPhone will take about 30 mins and involves using a programme called Redsn0w for your Mac or PC. Full details on the process are here. Follow them carefully and remember jailbreaking your phone will invalidate your warranty with Apple. When prompted you should choose to install Cydia.
2 Install Backgrounder to allow Spotify to work as a background process
Apple doesn't allow background processes (besides those provided by its own iPod app and some notifications) because of the battery drain. Be aware that you'll probably see your battery life shortened by making Spotify a background process.
With your jailbroken iPhone, download Backgrounder from here. With that installed and running simply open the app you want to keep open and hold down the home button. A prompt will pop up asking you if you want to let the app run in the background. Let go and exit and it will continue to run while you do other things.
3 Turning Spotify as background process off
If you find that your phone is running too slowly or behaving oddly, you can disable the app as a background process. Open Spotify and when it's loaded, hold down the menu button. A message will pop up to let you know it is no longer running as a background process.
Thanks to Nichola.