How can I convince my parents to let me get a cell phone?

i'm 11 years old and going 2 sixth grade next year,.... its the beginning of summer and all my friends recently got phones..but ME!!! i have an ipod that i can only text with, but only with wifi. and our internet is alwys acting up. if i get a phone, all i really would want to do is basiclly text, i dont plan to talk on the fone a lot. my 17 year old sister is ALWAYSS on the fone and goes over her limit. my parents say that i will try to copy her if i do. i really think i should get a cell phone...but my parents dont!! plz help