Sweet wishes to advise, if you have an iPhone 4 that is experiencing an issue with it's 'home button' - Apple will replace this free of charge if it is still under the 12 month Apple (manufacturer) warranty.
Be sure to resolve this issue whilst it's under warranty otherwise Apple won't "repair" your sexy iPhone but will charge you for a replacement, though they will swap it on the spot at your Genius Bar appointment.
Apple know the date you first registered your iPhone through iTunes, so all you need to do is:
1. Make an Apple Genius Bar appointment
2. Back up your iPhone the morning of your Genius Bar appointment
3. Arrive at your Genius Bar Appointment on time.