If one forgets their iPhone Lockscreen password, how would they go about getting it back?
Unfortunately there is no simple way of resetting the passcode without resetting the device itself.
The following knowledgebase article: http://support.apple.com/kb/ht1212 explains how you can reset the passcode by restoring the device from a recent backup. Even if the device is locked it will still sync with iTunes which allows you to restore the device which will delete all the data on the device.