Motorola E815 cell phone
This exact issue happened to me: I left my phone off for 2 days (unplugged), turned it back on and the internal speaker started working normally again. The phone worked normally for over a month after this.
Yesterday, the earpiece speaker stopped working again after the phone fell out of my pocket. I suspect a loose connection or something similar, but I've had my phone off for the last day and will let you know whether or not it starts working again.