There is no way to locate your cellphone if you have no idea where you may have lost it. The best thing to do is report it lost so that phone will be disabled. However, this does nothing for the information stored on your SIM card.

Should you find your phone or be forced to buy a new iPhone, you should install tracking software to help you find it in the future should you lose it again. Some are free others requires a subscription.

MobileMe is probably one of the best / better subscription tracking software. I can't say how good it really is or all of it's features. It is exclusively for iPhones. I use an Android phone.

Some tips: How to Find a Lost iPhone

http://www.wikihow.com/Find-a-Lost-iPhone

Of course given your current situation, you can only perform #7 and #8.


Good luck.