Sell now, or wait?

This question is actually a little more complicated than meets the eye...
As of now, I have a white iPhone 4S, 32 GB, with verizon. EBay's listings are going for about $300.00. I probably won't be selling on eBay, though. The last time I did that, PayPal held onto my money for 3 weeks before actually paying me. I can't go that long without a phone so i'll probably just use craigslist.
Anyways, if i wait until my contract expires, i'll be able to buy a phone in the middle of June. Just 3 or 4 months until the next iPhone. So, what do you guys think? Buy now or wait?