First, it's not your LG phone. You admitted you found it in a cab. At least you're willing to admit that.
Second, the phone will do you no good if you can't unlock it, and even if you do somehow, if the owner is smart they have turned it in as lost, the IMEI number is blacklisted and the phone is now a high-tech paperweight.
Third, people's lives are in their phones these days. All their information, photos - it's all there and is very valuable to them, value beyond the cost of the phone. Probably they have been calling the phone hoping someone will answer and return the phone. if you do the right thing and try to return it the rightful owner there could be a reward in it for you. We gave an honest person $100 for returning my wife's phone.
Fourth, if we tell you how to break into the phone it would be helping every dirtbag thief and finders keepers fool, encouraging more bad behavior.
If they call, answer the phone. Or if it's got a dead battery or no one's called do as Javier P. suggested and turn it in to the carrier. It's not doing you any good anyway.