How to make incoming calls NOT show up on phone bill?!?! PLEASE HELP!!?

ok so me & my bf dated for 3 years and were in highschool but our parents recently found out we had and me and my bf got in this huge fight from all the stress of not getting to see each other cause our parents found out & just how weird it was around our parents now and we ended up breakin up but only for like 4 days then we missed each other to much and got back together but when our parents found out we broke up they said we werent aloud to get back together cause of everything we had done so were keepin it a secret were dating again. i dont have a cell phone so i use my house phone to talk to my bf but it got turned off cause my mom has to pay the bill but wont have the money for another week so shes letting me use her cell to call my friends but said i cant call my bf cause she gets on the computer to look at the incoming & outgoing calls and ill be grounded for 3 weeks if i call him. she has AT&T so how can i call him or he call me to where it wont show his number on the bill thing? (she knows his,his sisters brothers & parents numbers) so he cant use those. please help we havent talked cept' at school in three days!!!