Have you jailbroken your phone? If so you can change all the ringtones, and take volume limit off with apps from Cydia.
If not in jailbreaking and unlocking, then you can search for some ringer software (I think alive?)_ that you can find on the net like mininova, customize your tone, and change volume there.
I have hacked a bunch of Iphones recently and volume has never been an issue afterwards
