How to persuade my parents to let me get a new phone?

Okay here's my story: I currently have an ordinary cell phone, nothing too extravagant. The deal was that next year when I graduate as a senior from my High school, my parents would get me a smart phone with the whole deal (internet unlimited txting etc), and they would pay for everything. I'm trying to convince my parents to get me a smart phone sometime this summer, but I want to give reasons and perks on why it would be better than my phone now. Any Suggestions..? Thanks!