Over on WowInsider, David Bowers presents an interesting conundrum. The gist of the article is that characters who hit 70 usually have greens and blues. If they want to PVP, it can take a very long time before they stand a chance against other characters who have been PVPing for a long time because these veterans generally have multiple epics. He goes on to ask, "How would you advise a new level 70 to get into PvP?"
I think there are a few solid ways that fresh level-70 characters can jump into the PVP game.
1. Do battlegrounds. The team in a battleground is much bigger than an arena team, so the fact that you are personally undergeared doesn't have as large an effect. Also, be sure to do the daily battleground quest for additional honor.
2. Craft your own epics. Choose professions according to your class, and craft away.
3. Do arenas anyway. They don't care arena gear "welfare epics" for nothing. Get in the ring and battle with the big dogs. The points will come slowly at first, but they will add up. Your feelings might get hurt by how badly you'll do, but you definitely will not regret it.
4. Socket your gear with Stamina gems and Resilience gems. I highly recommend [Steady Talasite]. They sell for 20g+ on the Auction House though, so if you can't afford those, I suggest [Solid Azure Moonstone].
Other than that, you're on your own! Good luck, and don't give up!