There is a registry edit you can do that will increase ringer volume. If you want to try that here are the instructions, follow them exactly, (at your own accord). If you do it exactly, you wont have any problems.
First off get a registry editor
http://www.phm.lu/Products/PocketPC/RegEdit/Install that on your phone, put the cab file onto your phone by connecting to your pc or mac, drag the cab onto your internal storage, open it, and install regeditor onto Internal storage.
Next, open PHM reg edit.
Follow these intructions: HKEY_CURRENT_USER\ControlPanel\SoundCategories\Ring (press the + sign to open each folder, and press on the word Ring to open it's contents)
in there you will see in the bottom half of the screen, something that reads InitVol, press that, and a new screen will pop up. Under Volume data it will read the number "3", change that (by using the up/down arrows), to something such as 7 or something and press OK, exit out, then restart your phone. Your ringer volume will be higher.