if you have the computer to which the iPhone has most recently synched, you can restore your phone from the most recent backup. This will remove the password, but any data between that synch and now will be lost.
If you don't have that computer, you'll have to put your iPhone in recovery mode (search this forum for instructions) and restore your phone as NEW. You will lose ALL data on the phone.
There's no way around this. If there were, there would be no reason to have a password in the first place.