Mobile iTunes uses the same acocunt that the iTunes of the computer's Wi-Fi it is connecting. That might have sounded confusing.
For instance:
My Mac has iTunes on it. On that iTunes, I am signed in as
jbanks290@gmail.com. My computer connects to the internet via a Wi-Fi router.
My iPhone is connected via that same router. Therefore, Mobile iTunes on my iPhone is also singed in as
jbanks290@gmail.com. Hope that helps.
- John