Earphones are the same, the sound quality is the same, depends on your earphones/headset.
my 2G was, and still is, louder than the 3G and 3GS i had on speaker (my mum is using my 2G now, loved the weight and metal casing and solid feeling of that 1st gen iPhone, none of them have felt the same since, in fact the plastic backed 3g and 3gs both crumbled in under a year, never bothered with either iPhone 4, to easy to break the glass, and the 5 chips paint like nothing on earth from what I've seen all my co-workers and friends who have shown me how there phones are doing now since launch)
only problem i had with the 2G was the little holes at the bottom for the 2nd speaker output/mic input kept filling with crap, so gently filed them out so each hole joined one of its neighbours, no crap in holes now, works fine and is loud both on speaker, and when held to the ear