Maybe AT&T Family Map can help you
To the original poster ... you do have one last possible hope if you are an AT&T customer (not sure if Verizon offers the same thing) ... it's called "AT&T Family Map" - a service that costs around $9.00 per month, which can be retroactively activated, and which can be canceled at any time (i.e., if you find your phone and after you've set up Find My iPhone).
This service works similarly to Find My iPhone in that it will locate your iPhone "IF" it is turned on (and if it hasn't been switched to a new SIM, which could be the case if it was stolen).
The reason I know this? Well, last August I purchased two new iPhone 4s two days before going on a month-long trip to Europe. I purchased MobileMe for mine because I remember losing my original iPhone2G a few years prior (which I did get back - that's another story) and at that time having a MobileMe account was the ONLY way to get access to Find My iPhone. Well, in the last minute rush to get everything done before going on my trip, I didn't get around to setting up MobileMe (which would have been step 1 before I could set up Find My iPhone). Needless to say, that I left my iPhone in the seat-back pocket of the very last airplane I was on in my homestate on the return. It was turned off as electronic devices are supposed to be on flights, so I was fearful that I'd never see it. I activated AT&T Family Map and started checking it every 15 minutes. A few days later, I finally saw that it showed up on the map - the airline flight attendant had taken it home with him and thought the battery was dead (not an owner and didn't exactly know how to turn it on initially - a friend helped him out). I had already sent text messages promising a $100 reward, so I fulfilled that promise to the guy, even though he was really just doing his job.
So, give AT&T Family Map a try. If it doesn't turn up any results after a few days, then turn it off.
Caveat: I don't know if you can turn on this feature if you only have one line on your account - we had two. It may not be a problem ... just saying since I don't know for sure.