We've already seen the dBCase that redirects sound from the iPhone 4's down-facing speakers to pump on the volume of the device, but if you're looking for something a bit more old school - or rather, olde school - to do the same job then the Horn Stand Amplifier might fit the bill. Made from flexible and washable silicone, the Horn Stand Amplifier borrows its form and function from the old-fashioned horn-speakers used on gramophones, slipping over the iPhone's speakers to channel the sound through the trumpet-shaped tube and supposedly increasing the idevice's volume by 13 decibels.
While the Horn Stand is quite a bit bulkier than the dbCase solution, it does also act as a stand in both vertical and horizontal orientations. Additionally, being non-powered, it won't place any extra drain on your iPhone's battery. Once in place, the device ends up covering quite a bit of the iPhone, including the home button, but includes a button to access the home button and a hole that provides access to the iPhone's dock connector. Could be just the gift for Grandma along with a few Benny Goodman tracks off the iTunes Store.
The Horn Stand Amplifier for iPhone 4 is available in a variety of colors from a number of retailers, including DealExtreme where it goes for US$5.60.