I use my iPhone exclusively for my audiobooks. I liberate them, then listen via Ambling Pro player, which has a great sleep function. At night I use my
sleepphones for listening, and during the day I either listen through the speaker in the iPhone, or via my Boombotix2 portable bluetooth speaker, or if I'm out, my Philips SHS8100 Earphones. I'd say I average 3-5 hours per day listening to audiobooks.