Question about Yahoo answers? 10 points?!?

Heyya rite so I've only just got the new iPhone 4. I use yahoo answers on my mobile, nd I've sold my old iPhone 3Gs to a girl at school. When you sign up it asks if you want the system to remember you so you will automatically sign in when you come onto yahoo answers. I allowed this, and I didn't sign out or anything when I sold it. So if I sign out on my new iPhone will it also sign out on my previous phone? Or if I deleted my yahoo answers account would it also delete it on my previous phone? Sorry about this but I don't want her reading my questions or anything, and as you can probably tell I get paranoid about things. Thanks, rosie :)