Ringo Pro

Another nice interface from the folks at Electric Pocket - and great functionality too. Pick ringtones or mp3 ringtones (uses built in mp3 player) for individual contacts or categories in your phone book. Also gives you individual sms tones and caller picture ids.

Price: $29.95

Phone Technician

I originally wrote this because I thought $30 was too much for mp3 ringtones. Phone Tech is one-ring-fits-all, though it adds extra features like scheduling when to turn on and off your phone connection and letting you turn off the screen during calls to save battery. It recently added the Sound Booster functionality, so it can now increase the volume of your phone calls. Phone Technician can use its own mp3 player on the treo 650+ or Pocket Tunes, MMPlayer or Aeroplayer.

Price: $14.95

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Surroundings prefs. (aka BrightCam)

One of those rare, unexpected and great ideas. Brightcam uses the camera to sense how dark or bright it is and adjusts your screen and keyboard brightness. It uses the microphone to sense how loud it is and adjusts your ringtone volume.

Most of the features are free (though please purchase to show your appreciation), though a couple of advanced features do require registration.

Price: free/$14.95

Volume Care Pro

Lets you set the microphone and speaker volumes on your treo beyond the standard maximum. Lets people hear you better and lets you hear them even in loud situations. Of course - overdoing it can blow your speakers!

NB - Although it doesn't have the level of configuration of Volume Card, Phone Technician can give you the basic function of allowing you to boost the volume of your calls.

Price: $19.95