I really want.... but my parents wont let me what can i do ?

i really want the INQ Chat 3G phone, on 3 for onl �10 a month with unlimited texts and 75 minutes, free twiter and so on, but i get �15 a month pocket money and my mum and dad wont let me get it coz i will only have �5 a month, i need ideas to help me persuade them to let me get it, i was thinking of me paying �5 and them paying �5 ? what do u think, the offer ends on the 31st march, please give me so ideas :)