How do i get me mom to get me a new cell phone!?

Hay i have the verizon prepaid blitz and it sucks! please help me convince my mom to get me and my sis the t-mobile gravity! we could both be on the family plan and share 2500 minutes for only $70 a month! and its not that my mom doesn't want me to have a phone yet because i had one when i was 6! answer ppppllllleeeeaaeeee