I had this problem in the summer, didn't want to take my laptop on holiday just my iPad and iphone, but found an app called Tango Remote. Just search for it on the App Store. It's exactly what I wanted, can control the music playing from your iPad with your iphone and in reverse, both have to have the app open and linked to the wireless network. It sometimes crashed when connecting each other but you just need to shut the app down and start again. Well worth a look!