I'm sorry, but in my opinion, you are too young. What is your argument for getting one? So you can fit in with all of your friends? So you're parents know where you're at? For safety?
I was 18, off at college when I got mine and had a job so I could pay for it on my own. Sure, all of my friends had them before me, but it wasn't the end of the world. If I missed the bus, or if I was going to be late, the nice thing was that most of my friend's had cell phones, so i'd just call from that. Who cares if its embarassing, you won't die.
And "safety"-wise, that's a bunch of baloney. At 13 years old, where are you seriously going to be that someone responsible will not be with you? You're not driving yet, so you can't get stranded or break down.
What did people do before cell phones? Landlines and pay phones. I realize that there are no more pay phones, but seriously, there's ALWAYS a land line. Unless you're in the middle of no where, which I'm highly doubting would happen at your age. If you're truly in trouble, there will always be people around to help.
Try looking into a Firefly. Given it doesn't have texting, or anything fancy or cool, but it gets the job done, right? It makes calls to only those your parents program into it, which is the only reason you would need one, right? Then maybe when you turn 14 or 15, you can get a job and pay for your own cell phone, yes?
In the end, its your parents' decision. If you keep bugging, it will just upset them and give them reasons to NOT get you one. Show you're maturity by NOT asking for one like the rest of your friends. In the end, they'll appreciate you for it.