Quite a few Nokia models (beyond the two listed above) have a great feature that makes these phone much more useable in noisy environments (such as crowded shopping malls or while walking down a busy street). When the phone detects that you are in an especially noisy area it boosts the volume of the earpiece by upwards of 5 dB (this value is an educated guess). It doesn't even matter if you already have the phoned cranked up to full volume, as the level will still be boosted.
On recent tests I performed with the 6310i, the extent to which this feature worked was amply demonstrated. I stood on the Mavis bridge over Highway 403 in Mississauga during rush hour, which is a pretty noisy place to be. Just to speak with someone standing next to you, it would be necessary to raise your voice to the point of almost shouting. I then called 611 on Fido to listen to the front-end recordings. As many Fido users know, these recordings are not especially loud, and it is even worse in Mississauga, as that area is served by Nortel equipped sites, which are noticeable fainter than the Ericsson sites still found in many other places in Southern Ontario. Despite all that, the phone boosted the volume high enough that I could hear every word spoken without straining to do so.