The tap to control music button is right next to the power button, and it is a little tricky figuring out which is which. (indianexpress.com)
Like Sony's old Walkman phones, the Xperia E1 has a dedicated music button up top. (techradar.com)
(Some people say Kickstarter's music buttons don't show up for them, so here's the link to Sneaky Ninja's SoundCloud page where you can listen to all the songs including new ones added in updates!) (kickstarter.com)