I'm now on my second iPhone. I returned my first one and replaced it with my new one. The volume on the new phone is better than the old one I returned, but not by much. However, it was still worth swapping them out.
When the iPhone is placed up to Max volume, it should be so loud that most people would never use it. However, maxing it out makes it just barely usable.
Part of the problem lies with the ridiculous ringtones they put on it. Items such as "Timba" and "Blues" are barely heard on loud. I'd recommend for the time being to play with the diffrent ringers and not pick the one you like to listen to the best, but instead pick the loudest one. I now have mine set to "Trill" which makes quite a difference.
Apple needs to let its users create their own ringtones and/or download alternatives. My previous ringtone was the Imperial March from Star Wars. I chose it because it was powerful and loud which meant I could leave it on the table upstairs, be outside downstairs and still hear it ring. With the iPhone, I had it sitting on my desk at work and couldn't even hear it ring right in front of me on Max volume!!! Thus, providing the users with different ring tones might make a huge difference as well.
I honestly don't know how they can expect the volume to be sufficient when in the Apple store today, there is no way anyone could have heard an iPhone ring. There were at least 100-200 people in the store and with the talking, there is no way anyone could have heard an iPhone ring unless it was on vibrate or they were holding it right next to their ear. Completely unacceptable. What good is a phone if you can't even hear it ring? It's like having a Ferrari, but no gas to put in it.
As one other piece of info (for those who may be unaware), when listening to your voicemails, if they sound really, really low, try hitting the "Speaker" button on the upper right hand side of that screen. You can hear the VM message faintly without hitting the speaker button, so many might think that they are being played back on the speaker since you can hear something.
All in the all, the iPhone is great. However, the volume issue needs to be addressed and Apple needs to take care of the customers who have already been dealing with this issue.
Cheers.