After installing my first App I realized I wanted to update my appleID email address to a more current email. So I logged into the iTunes store and updated the email address in my account info. I wasn't sure if this would somehow reflect on my iphone next time I used it or tried installing an app. Each time I was prompted for a password, my username (appleId) was still the old one. It was not until I hooked the iphone up to iTunes and did a SYNC did the appleID I want to use started showing up on my iPhone.